Hello,
I believe the distribution Type such as PAY/PURCH is used to correlate the amounts from the document to the distribution window, as Elena suggested. It is also used to help find the default posting account for that distribution line. So if you change the GL account after the fact, that should be fine and still post correctly. *
If you change the PAY/PURCH types, there is a verification that the amounts for each type need to sum up to the original amount on the document, so you may get errors on the validation. The distribution lines for TAX need to total the tax amount on the document, the PURCH line needs to match the amount in the PURCHASES field on the document, the PAY line needs to total the TOTAL or net paid amount on the document, etc...
*If you change the GL accounts and leave the PAY/PURCH, please note that the 'reconcile to GL' utility uses the PAY/REC lines to pull distributions on to the Excel spreadsheet, so if you use this tool to help reconcile RM or PM to GL, it could impact that tool. (which is only an 'aid' to help reconcile). You can read more about that in 'Q8' in the 3rd bullet at the bottom of this KB article:
support.microsoft.com/.../866570
Hope that helps. Please mark as 'answer' if this is helpful to you.
Thank you,
Cheryl Waswick
Microsoft Support