After entering a document can you delete the entry? Can you change the document? Which fields? can/not is changed?

1) After entering the doc we can change and we can Delete it
2) After posting the doc we can't delete it only we can revers it 

and Some of Fields we can Change those are

a) Assignment No
b) Value date
c) Text ONLY

But remember we cant change the amount once you posted.
Where as in AR & AP we can change Discount base amount, 
Base line date & payment terms.

We can delete the account before we post any entry in 
the account.For that we have to create deletion flag...