You can change the tempo of a song in the FA-06/08 using the TEMPO knob on the front panel, but it is also possible to add tempo changes using the Microscope mode - and this is how it is possible to have tempo changes within a song.
- Press SEQUENCER so it is lit.
- Hold SHIFT and press the #5 button (which says "Microscope" on the screen above it).
- Press the #7 button (which says "View" above it on the screen), then turn the value dial to select the TEMPO track and press the #7 (Close) button. You can now see all of the tempo messages.
To create a tempo change, press the #2 button (which says "Create" above it on the screen), then press the #7 button (which says Execute above it on the screen). Use the value dial and the cursor buttons to select the location (measure / beat / tick) for your change and then press the #7 (Execute) again. You can now cursor to the tempo amount and use the dial to change it as desired.
To erase a tempo change, first select it in the screen, then press the #3 button (which says "Erase" above it on the screen).
There are also options here to Move, Copy, and Paste tempo changes, so it is certainly possible to add multiple changes within a song.