The two cases MtG I know of off hand are to do with accidentally broken rules updates. One was when the added a moment "between turns" where you could activate

The two cases MtG I know of off hand are to do with accidentally broken rules updates. One was when the added a moment "between turns" where you could activate abilities but not cast spells (added to make Time Vault work). The interpretation that you could activate wall of roots infinitely is similar to the chess cases you're pointing at ("once per turn doesn't constrain what I do between turns"). The other was Yawgs Will exiling effect was briefly a triggered effect instead of a replacement effect which let Yawgs Will + Dark Ritual also be a trivial infinite, which wasn't even rules lawyering it just was so clearly broken and unintended that Arbiters didn't allow the official rules and eratta to ride. But really I don't think any of the rules of chess ever unambiguously allowed either of the things you said, they are both extreme rules lawyering primarily known for their humorous value, and the rules being clarified they aren't allowed doesn't prove they were allowed before. E.g. 0-0-0-0-0 claimed a pawn promoted to a rook is "a piece that hasn't moved", and easily could have been rejected as saying it is the same piece that moved while it was a pawn. En Passant is widely know and explicitly specified in the rules, taught, and played by even low level players, so there's no way it's similar. I think it's impossible to know unless you can find a case where someone actually attempted the moves, but I feel pretty confident they just wouldn't have been allowed and if you tried a similar gag at a rated chess event today the arbiter would just tell you that you're crazy.