user47827: Given OP_VER (0x62) was never used onchain, is disabled and is not considered useful can its meaning be stripped and it be made OP_SUCCESS for the purposes of introducing a new different opcode in future?
As Andrew Poelstra describes "..there was an opcode called OP_VER, OP version. I can see some grimaces. It would push the client version onto the stack. This meant that when you upgraded Bitcoin say from 0.1 to 0.2, that’s a hard fork. Now script will execute OP_VER and push 0.1 onto the stack for some people and 0.2 onto the stack for other people. You’ve forked your chain. Fortunately nobody ever used this opcode which is good. "

user101498: Since it was set to an error by Satoshi and not a SUCCESS, this would be a hardfork for all clients in-between no matter if this was already used onchain before.
Just imagine a miner with the new software (which redefines VER as SUCCESS) mining a transaction containing such an OP. All the clients between 0.3.5 and the new one would refuse the block, while all the updated ones would accept it: chain split.

user47827: BIP 342 does exactly this. (Thanks Pieter)

47827: <p>Given OP_VER (0x62) was never used onchain, is disabled and is not considered useful can its meaning be stripped and it be made OP_SUCCESS for the purposes of introducing a new different opcode in future?</p>
<p>As Andrew Poelstra <a href="https://diyhpl.us/wiki/transcripts/london-bitcoin-devs/2020-02-04-andrew-poelstra-miniscript/" rel="nofollow noreferrer">describes</a> &quot;..there was an opcode called OP_VER, OP version. I can see some grimaces. It would push the client version onto the stack. This meant that when you upgraded Bitcoin say from 0.1 to 0.2, that’s a hard fork. Now script will execute OP_VER and push 0.1 onto the stack for some people and 0.2 onto the stack for other people. You’ve forked your chain. Fortunately nobody ever used this opcode which is good. &quot;</p>
 101498: <p>Since it was set to an error by Satoshi and not a SUCCESS, this would be a hardfork for all clients in-between no matter if this was already used onchain before.</p>
<p>Just imagine a miner with the new software (which redefines VER as SUCCESS) mining a transaction containing such an OP. All the clients between <code>0.3.5</code> and the new one would refuse the block, while all the updated ones would accept it: chain split.</p>
 47827: <p><a href="https://github.com/bitcoin/bips/blob/master/bip-0342.mediawiki#specification" rel="nofollow noreferrer">BIP 342</a> does exactly this. (Thanks Pieter)</p>
