A quick google search throws up this, which may be a good starting point:
http://www.ukweather.freeserve.co.uk/metarpg.htm Or
Decoding a TAF
I've not seen COMPLETE before, but TEMPO (and INTER) have specific meanings - for TEMPO, the conditions may persist for up to an hour, INTER up to 30 mins. They do not change the base forecast, they're used for temporary phenomena.
I would read your taf as "COMPLETE... BECOMING" and the tempo's as temporary changes - it's rather odd that the TAF ends at the same time as the second tempo kicks in.