I will offer one of those opinions which Jock mentioned. Wearing the tartan of a clan with which one has no affiliation is not a hanging offense. It is not illegal at all. However, the matters of propriety and good taste are quite apart from legality.

Should you wear the tartan and be asked by someone who recognizes it about your affiliation with the clan, how will you answer without causing embarrassment to yourself or to the questioner? If you have a suitable reason, or if respect is simply of no consequence to you, then there is no need to be concerned about it. The inquirer is not likely to pursue further conversation.