、。
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].
万が一 ('one in ten thousand') is the slightly more emphatic variant of 万一 — the inserted が gives the phrase a measured, deliberative feel. Combined with 気が変わる ('one's mood changes' — the idiomatic 'change one's mind'), it sets up a polite request to be informed if a remote possibility happens to materialize.