Should the customer want to change something himself he could reprogram it in basic.
I doubt very much that the "customer" we are talking about has any knowledge of basic. (S)he will, of course, have no knowledge of ladder logic either. However arguing basic vs ladder require the customer knowing either. The reverse argument goes for industrial equipment wher there is a broad knowledge of ladder and virtually none of basic.

Should the order increase from qty 1 to qty 10 ...
All PLC suggestions have been prefaced with "qty 1"

Editorializing:
Many of us did/do forget about the cost of time. While time may be "free" for an amateur, Ronan indicate he is making this thing for money. He may, of course, still consider his time "free", but that is the sure way to ruin.

Erik