Yes it would be possible to do both of those, I hadn't even considered deleting notes, I just concentrated on the problem at hand.
In the first case it would involve "searching" the memo field first for a date either side of one you wanted to insert, when found you would "split" the memo field with the new data.(memo = left(memo) & linefeed & linefeed & newdata and linefeed & right(memo)
In the case of deletions you would find the "note" match in the memo using the instring function and then just replace it with the word "deleted", so that there is a record of the deletion.