Hi dude,
I suspect over-training any function would lead to deterioration in other areas; notably those least frequently used by the individual. Time spent practicing one thing is time lost practicing something else. I'd expect least used connections to go first, although obviously there are tons of confounding variables; like nutrition, starting state of the individual, amount of sleep, anxiety levels, etc etc so everyone would be different. Someone who uses creative skills every day isn't going to lose much by practicing worrking memory training. But someone who hardly ever uses their creativity could well lose it.

It's a bit like dedicating yourself to working out only one arm. If you still use all the pther limbs, you just end up with one bigger arm. But if you totally stop using the other limbs in order to work on the chosen arm, they will deteriorate.
Best,
AR
PS excuse typos, I have way too much to do today and more haste always causes yzxdtkbs.