#1
I have a 2x12 cab that I'm pleased with, but want to change speakers around a bit. I noticed the cab rating is only 120 watts, and I'm wondering how important it is that I stay at or below that. Can I put for example a 60 watt/75watt speaker combo totaling 135 watt? Could I put 2 90 watt speakers, totaling 180 watts? Or am I risking damaging something? I just recently aquired a really nice amp head, so I'm not wanting to damage it.
#2
The cab rating is directly related to the wattage of the speakers inside. Increasing the speaker wattage increases the rating of the cabinet.

Mad Professor Snow White Auto Wah
TC Electronic PolyTune 2 Noir
Joyo Vintage Overdrive
ZVex Box of Rock
Chase Bliss Audio Warped Vinyl
TC Electronic Flashback
Neunaber Seraphim + EXP
Hotone Wally
#4
Sure tsuzu01. The new cab rating will be the lowest rated speaker multiplied by the number of speaker, e.g. 150 W x 2 speakers = approx. 300 W cab.

Make sure to double check the ohms on the speakers you're getting too.

See the link below for more information.
http://celestion.com/speakerworld/guitartech/1/37/Speaker_Upgrade:_Power_Handling/

Mad Professor Snow White Auto Wah
TC Electronic PolyTune 2 Noir
Joyo Vintage Overdrive
ZVex Box of Rock
Chase Bliss Audio Warped Vinyl
TC Electronic Flashback
Neunaber Seraphim + EXP
Hotone Wally