Other known variants
x2Energy Trans
As often as you like during your turn (before your attack), you may take 1 Grass Energy card attached to 1 of your Pokémon and attach it to a different one. This power can't be used if Venusaur is affected by a Special Condition.
SolarbeamThis plant blooms when it is absorbing solar energy. It stays on the move to seek sunlight.
Can you "Energy Trans" or "Dark Trance" a Rainbow Energy, Multi Energy, or any other special energy cards?
As long as they are providing the proper energy type and don't violate any other restrictions written on the card, then yes you may.
In Team Battle, can I use my Venusaur to switch Grass Energy between my teammate's Pokemon (not moving them between owners)?
Yes.
If Porygon2 has changed a Grass energy to Lightning, would it be fair to say that Venusaur could not Energy Trans it (for the rest of the turn)?
Correct.
Can Venusaur put other energies on Fire Pokémon?
Only other grass energy.