It should never allow you to reemplace a transaction, or to change outputs,
it should allow you to give more priority to a transaction that it's stuck on the limbo of 0 fee/smaller fee transactions.
Only replace the transaction if it's the same transaction with bigger fee. to the same outputs.
Any other thing is not bitcoin, btc is not reversible.
or you just killed satoshi dice.
Bitcoin is a system for deciding which of two or more transactions is the "right" one. We use a global network and consume quadrillions of hashes every few minutes not for our own amusement, but because the problem really
is that hard.
A transaction is exactly as secure as the quantity of work it would take to reverse it. Zero work? Zero security.
STOP ACCEPTING ZERO WORK TRANSACTIONS. You've spent too long in dreamland, assuming that the intention to hash in the future was as good as hashes already done in the past. They aren't, they never were, and now everyone will be forced to accept reality as it is.
But talking about improving you could also change the 10 min confirmation to 2 and slash the rewards 5 times.
then they will change to a 1or 2 confirmations .
Confirmations don't secure transactions. Hashes do. Making the blocks more frequent would mean that they have correspondingly fewer hashes of security. Changing the lump size that hashes come in won't help anyone.