May I suggest to define a specific Division and Project for the accounts as same as ability to define TAX code for these accounts.
I can select division for the customer but I need to separate the revenues from one of my customers by divisions as I’m providing services for this customer in deferent location “which are a deferent divisions” and also I provide these services for him according to different contracts which are “different projects”.
Currently I must select project and divisions for each invoice line and that would be more handy to define these choices like defined TAX code “automatically”.
Concerning inventory and non-inventory items which have a defined account we should be able to change accounts or projects and decisions in invoice’s line after applying the default defined account or project and division.
Now we can not change the default define account for the invoice line items.
None of your suggestions is possible. Projects are linked to ledger entries, not to the accounts where they are posted. And assignment of inventory items to divisions and accounts cannot be changed because, in Manager’s design, inventory items are subsidiary ledgers. In other words, a division selected for an inventory item owns the item. You cannot randomly assign transactions buying or selling it to different ownership. Likewise, non-inventory items cannot be changed at will, because their assignments to divisions, income and expense accounts, or tax codes are fundamental characteristics of the item. Changing any of these changes the item, so you lose control; and control and standardization of the item is the entire purpose for creating it.
Nothing is impossible, if the projects are linked only to ledger entries, I’m asking to improve it to link with the accounts I post to it to. I’m asking for more control over the use of project assignments for accounts. this is the fact.
Going back to my first example on the topic: I provide over 2,500 different services “non-inventory items” to just one customer and I provide these services in more than one city “which is a different department”. The other option now is to create a different account for the same customer, each following one of divisions to allocate revenue from him according to the divisions, but what do I do with 2500 services provided to this customer according to multiple contracts with him “we are talking about 10,000 services at different prices with the same customer”?! Do I copy these services and repeat them also with the number of divisions?! it would give me more than 30,000 item and of course, this is illogical.
Now the need is to facilitate the process of allocating divisions and projects on the invoice line, as the invoice sometimes consists of more than 30 lines and I am forced to redefine the project and division for each line in them.
Would you suggest me a better workflow?
That may be true. But what you think is a simple software change is a major reconceptualization of the program. So I would not hold my breath waiting for it to happen. That just is not the developer’s vision.
I would advise to use another application to do your inventory management and invoicing and use manager only for summary entries for tax accounting purposes. This is similar to why retailers and similar are advised by @Lubos and others including myself to use a dedicated pos system from which you export the totals into Manager. Reason being that Manager eventually will slow down when dealing with large numbers of transactions.
Actually I don’t have problems with inventory items, currently my business depends on non-inventory items. So I do not have any quantities for inventory items I do have about 1000 item. But because all of it rated with zero price. I do not use it for invoicing.
I’m using Manager normally, there is no large number of transactions. So, It’s very disappointing to be advised to use a POS to manage my inventory while I’m asking for another help to makes invoicing more handy while defining the project and division to the sales invoice line.
Generally, I hope this will be available even if it is not the developer vision at the moment. I hope he will think about it now or later.
Thanks @Tut and you @eko for your attention. 
Please read carefully, I did not say you need to use a POS, I mentioned that when transactions are many you need to use it. I also did not distinguish between non-inventory and inventory items, but being fully aware like myself that you use inventory for services. However, I think that even then your numbers are far beyond the scope of a small business program like Manager, hence the advise to seek fro something that will meet your scale.
You makes me confused more and more. I’m suggesting to improve projects and divisions to be defined for COA. nothing in this topic is about my business size.
Thanks again for your valued look at our business. Don’t let the numbers and size of the inventory and services I provide cheat you, We’re classified under small and medium-sized business in KSA. Even the developer himself always denies your opinion here that Manager is only suitable for small businesses.
I guess you don’t need me to quote many posts where he denied that.
However, I know that your advice to find an accounting system that suits us comes from your experience and I appreciated for that. Thank you for your sincerity.
What I really asking for is to discuss the project and divisions defining process for each line in the invoice.
Actually that would be useful as the last time I actually hinted that it would be not for small business I was corrected and even referred to the home screen (see screenshot below)
There are a lot of things pretty well sorted with Manager and I like the user-interface and the flexibility. But is has its limitations in the way it has focussed to be very quick and efficient in what it does well, but in my view and supported by the developer it does not scale well.