Increasing Global Rate without Affecting OLD Billed Invoices

[LifestyleDesigner]

Is there any way to LOCK invoices once they are billed?

It's a new year and I'm increasing my rate, but my billed invoices from last year all recalculate to NEW rate.

I'd really like all invoices to LOCK once billed and not be affected by changes.

The only thing I can think of doing is creating NEW clients with independent rules ... but that doesn't allow me to set some defaults like minimum time, which only seems to be a global choice.

[Adam]

Rates are always locked in when you create a Time Entry.  They will NOT change unless you change the rate in the entry itself.  Changing the Global, Client, etc rates will NOT change existing items.