[richiebee]

ALL rules in music are optional.

Songs can change tempo. Changes are more acceptable in some genres of music than others. The change should make sense.

In the context of tempo, I would recommend that you keep it simple. Otherwise you just confuse people, and they stop listening to your music!

Gradual tempo changes (upto about 5bpm) are practically unnoticable by a non-musician and can help project a song.

Sudden changes of a much more drastic nature can be very effective in the right song.

Doubling or halving the tempo makes life simple for the listener and can help them to continue to dance when the band has gone into a frenzy.