* Pre-: This means "before" or "prior to", so you could use it to indicate something that is pre-finished, meaning it is finished before a specific process.
* Post-: This means "after", so something post-finished would be finished after a specific process.
* Re-: This means "again" or "repeatedly", so something re-finished would be finished again.
You could also use prefixes like un- or de- to indicate the opposite of "finished", like unfinished or defaced.
Ultimately, the best prefix to use depends on the specific context and what you want to convey.