At the end of Timeslides, we see that the changes Rimmer make to the past mean:
He becomes human again
Obviously this is just a gag, because seconds later:
he blows up, becoming dead again
and in the next episode he's back to normal.
Despite this being an obvious joke, discrepancies like this are sometimes still discussed or explained (see the opening crawl for Season 3 episode 1).
So it still stands how could his changes in the past have made that happen?