Changing targets if a permanent has ward and you didn't realize it

As a preface, I took a 6 year break from mtg as a whole and got back into EDH around 3 months ago.

Tl;dr: Do you let people change the target of a spell or ability that is targeting something with ward? Technically you can't, given it is a triggered ability but I'm playing more laid back commander and it is commander with 50 different effects and triggers flying around, so I don't mind letting someone change their target if they forgot personally.

Something I've seen come up twice now is when someone targets a permanent with ward, the player controlling the ward creature will complain that you technically can't change the target because ward is a triggered ability. The first time was at my LGS at a table where all of us were playing middling power decks, generally a bit better than a decent precon. The player with the ward creature (which was his commander) told the whole table at the beginning of the game that if you were to target his commander and forget about ward, he wouldn't let you change the target because it is a triggered ability. I didn't really mind this because he did make it very clear from the onset and it was a great couple of games we played.

The second time this has come up was when I was playing on spell table. Three of us were playing some more casual decks we'd built ourselves while the fourth person was running a high power deck running things including mana drain, cyclonic rift, fetch lands etc. I was playing [[The Watcher in the Water]] and was targeting something with a stun counter and one of those creatures had ward and I targeted it. I was tapped out otherwise and when they mentioned ward, I asked if I could change the target to something else. I was then lectured about "doing my research" and how I should know how it works. He then won using an infinite combo on his next turn. I found this frustrating given they downplayed the potency of their deck before the game and then won the next turn regardless. I know I technically was unable to change the target but it just seemed rude and out of touch to me lol

Anyways I'd like to know you guys' thoughts on ward, I personally don't have a problem with it even when ward is on one of my creatures, but you guys might think differently. Thanks for reading :)