、。
If you happen to change your mind, please let me know.
Literal
By-chance spirit [subject-が] changed-[conditional-たら], inform-[polite request-て下さい].
気が変わる ('spirit/mood changes') is the idiomatic 'change one's mind' construction — the feeling is the grammatical subject (a 'change' that happens to you), conveying involuntariness. Compare with 考えを変える ('change one's thought'), where the thought is the direct object — that framing sounds more deliberate. The 万一 + ~たら opening is a soft, polite hedge for a request: 'just in case X happens, please...'