So are you "saying" that it's possible to send bitcoins to an exchange like for example MEXC and then "fool" them by having the script delay the "ownership" by say 10000 blocks... and then if MEXC falls for it and credits the attempt with on exchange credit then later the owner of btc can reverse the transaction 
I think you should read a bit about the possibilities for contracts provided by Bitcoin Script and Tapscript (see this wiki page for example). Lightning Network and many other technologies are built on quite similar contracts with timelocks and hashlocks (where you have to provide a secret string to unlock a transaction).As @stwenhao pointed out already and it would be a P2(W)SH or P2TR transaction so it would not be possible to send coins using this method to standard deposit addresses of exchanges. Instead, it would be sent to a special address, which could be compared to the "contract addresses" in Ethereum for example. You wouldn't be able to deposit this way, as of early 2025, on most or all existing exchanges. Of course this kind of contract would be also publicly visible so it would be very difficult to scam somebody this way, but that's of course not the idea, see below.
Reversing the transaction in this case, would mean posting another transaction, before the 6th block... so before the script activates...
This is correct, you could describe this as a "drawback" due to the fees. A transaction to transfer the funds from this "contract" to another address can be "posted" by the sender (since it was sent) and by the receiver (since the "undo block", e.g. 6 or 10000 blocks after confirmation).Also this idea is not to scam people, it's kinda the opposite of this... people could force other people to make rushed decisions, for example exchange seizes to exists... and people make plenty of typoes...
Exactly this would be the purpose of this kind of transaction. I could imagine it to make sense in some cases. However, the merchants always have to support it.(LOL: Imagine Binance says: we're shutting down in 5 minutes ! if not withdrawn by then, all funds losts/seized by us, bye bye ! =D If you have only bitcoin, maybe... if you have multiple coins, oops, no time to check nothing... gogogogogogoggo)
I don't really understand how this is related with the "undo transaction" protocol. What you describe would not even need a Bitcoin Script contract. It is also not possible to allow, via Bitcoin Script, to create a transaction only until a certain block. All you can do is setting a start block from which a transaction or output becomes available (methods are: CLTV, CSV and the standard Locktime), but you can't set an "end block". In the case of the "undo transaction protocol" I proposed, the transaction can be reversed also after more than 6 blocks, but then the other side (the receiver) would also be able to transfer the coins.