"I'd like to create a register to manage prepaid expenses for my clients, by using the same logic as fixed assets, but using prepaid asset accounts."
We have several clients that use AssetAccountant™ to manage Prepaid Expenses.
This is done by creating an Asset Group in AssetAccountant™ specifically for prepaid expenses.
If you are using a partner integration (i.e. Xero or QuickBooks Online), map the new asset group to the General Ledger accounts on that basis.
The accounts should be able to be mapped to any P&L or Balance Sheet accounts you have set up in the GL.
Note for integrations: While they may still be named the same at AssetAccountant™'s end (e.g. Depreciation Expense), these are really just placeholder names and you should have the flexibility to map these to any accounts that make sense to you.
Feel free to create a new AA register, play around with some account mappings, try setting up a prepaid expense then creating a journal.
If it doesn't work the way you expect, you can simply rollback the journal and archive the register (in Register Settings > General).