Can you transmute before taking energy tokens?
No, as you have to to receive energy tokens from your crystal before doing anything else. From the 2nd edition English rulebook, p. 8, emphasis mine:

Resolution order of the actions of the player’s rounds
The following actions on the Seasons dice must always be resolved before performing any other action: drawing a card, receiving energy tokens or crystals, increasing your Summoning Gauge. Once these actions are resolved, the players can perform their other actions, in the order of their choice.

After that, you may transmute at anytime and as many times you want during your turn.