If a creator allows NFT owners to change traits of their NFT and that affects the rarity score of my NFT, do I have a right of remedy?

No, if the right of modification was given by the license issued by the creator himself to
the NFT holders, the latter’s have the right to use, enjoy and dispose of the thing as an
intellectual property right has been licensed (that would vary accordingly to each license
conceded though). In that regard, the license applies as a legal agreement between parties,
and it would have the force of the law itself, pursuant to article 421 of the Brazilian Civil Code.

Most likely no.

A remedy is available depending on the terms of the contract. Where a valid
purchase occurs, the law will recognise some equitable remedy at least.

Everything depends on the specific terms of the contract between the parties. There is a scenario in which the seller of the NFT token may be liable if the buyer of the NFT was misled and/or deceived about its characteristics.