Interesting idea - I've wanted to be able to swap Mind for Agility skill slots, or vice versa, but hadn't really given any thought about how to do it.
Two things jump out at me about these advantages. First is the limit that you can only take it with an Agility / Mind of 2 or less. Maybe someone is really bright, Mind 4, but never had a chance to learn academic skills (a traveler from a less educated region or time period, etc.), but was instead taught in the hunter/gatherer skills of his people and wants to trade 2 Mind skills for some practice at climbing and stealth. That seems to be something BASH doesn't currently handle, since the Unskilled disadvantage affects both stats and also increases some other penalties. It seems like the new Jock advantage would fit the concept nicely, but couldn't be used because of the max stat limitation. Would a limit of no more than 2 skills being swapped work instead?
My second concern is, frankly, purely balance related, so its importance would depend on how concerned you are about that. There's the optional rule that equates an advantage with 1 character point, where you can buy extra advantages for 1 point each. But you can also use 1 point to buy the Skillful power which gives you 2 extra skill slots. So, from a purely min/max perspective, you could either "spend" 1 point (or advantage slot) to swap 1 or 2 skills between your stats, or you could take Skillful and gain 2 additional skills (without giving up any in the other stat) for the same "cost". For myself, flavor generally trumps optimization, so I wouldn't avoid these advantages just based on min/maxing; if a character concept works with these advantages then that is more important than optimization. But I thought I'd point out the issue, in case it sparks some other ideas.
Part of me wonders if it really qualifies as an advantage at all. You're not actually "gaining" extra skill slots. At most you are gaining a bit of flexibility, and you gain much less benefit from this than you would from other advantages like Jack of All Trades, etc.
Maybe you just need to provide a justification to the GM, with an in-character reason to explain why, and you could swap up to 2 skills from one stat to the other for free.
I don't know, I really don't have a good suggestion or alternate solution that is particularly convincing to me either...
