You may be able to use Class Designer devices and set one for default, one for health and one for shields and hook your buttons up to 2 Class Selector Volumes for switching between.
This achieves full health and shield instantly, but I am not sure if it will work how you want, it can give full health and no shield, but in regards to one giving full shield without affecting the health I am not sure.
Verse could be a better solution if you find an appropriate tutorial