In version 2.4, when you create a project contract milestone it currently locks some fields on the form that I think should stay open including:
1. Milestone Name
2. Milestone Date
3. Line Amount

I did the following in our environment:
1. Changed fields to not be read-only on the form
2. Setup business rule that locked these fields when the Invoice Status changed to NOT EQUAL - "Not Ready for invoicing"

This allows a lot more flexibility to change amounts, dates and description without having to delete and re-add.

Thanks,

Drew