Currently I am unaware of any method to do this. On the plus side, you only have to do something like that only once, and then just periodically do it with the rewards as you get them. On the downside, everyone only has to do this once, and it doesn’t impact new players, so we may not see this put into the game (if it isn’t already in place)
There's no option to transmute multiple at a time, but if you're on Droid I highly recommend this thread: https://forum.kingdomsatwar.com/thr...-to-improve-kaw-experience-on-android.163667/ Using the settings as described in that thread make transmuting happen instantly when you press the transmute button, rather than waiting numerous seconds for the bar to fill and confirm the action.
No clue if there's an equivalent iOS setting actually. Probably a good chance if you're jailbroken (is that still a thing?), but somehow I doubt Apple's defaults let you change that sort of thing. Maybe you should play on a more flexible OS, Fox.