QBP: Using Credit Memos to apply pre-payments made by Client

[EDIT] Ignore this question. I was reluctant to experiment for fear I would do something that couldn't be undone, but I went ahead and experimented anyway.

I decided to experiment and discovered that if you apply part of a pre-payment transaction (from "other payments") to an invoice, QBP automatically turns the rest of that payment transaction into a Credit Memo. Which is what I was trying to achieve in the first place.

The situation:

• Client pre-pays for certain work to be done on a Project
• Work is done for the Project and expenses are ready to be Invoiced
• I want to apply the Client's pre-payment to the Invoice

Is this what Credit Memos should be used for? How can a new Credit Memo be linked to an existing transaction? Or is it better just to use the "Other Payments" that are available in the Sales History?