I updated to the latest version of CSSU Thumb this morning and tested FMTX. FMTX (including changing and saving frequency) seems to work fine for me.

For what it's worth, I have the old Jacekowski.org FMTX fixes installed. I do remember that if you miss an installation step (http://talk.maemo.org/showthread.php?t=60567), the newly accessible 76 - 88 MHz range will be visible but inoperable.