Crimson Longinus
Legend
Well, the spell versatility goes far beyond that, it allows swapping spells on every long rest.I've always been a fan of rebuilding and retraining rules generally.
Buyers remorse is not fun. The game loses nothing by allowing such swaps later on (as long as there is a slight opportunity cost or time limit to be served to so switch).
And whilst it makes sense to allow some amount of rebuilding, I think that just shouldn't be the default approach and should be agreed with the GM on case by case basis. It is just weird for characters to forget abilities they used to have and it can also encourage bizarre min-maxing (this feature is good at these levels, but then I get that feat on the higher level I swap it to this other one.) Perhaps some people don't mind that, but It kinda rubs me the wrong way.