That could definitely work as an idea. I think it would be nice to be able to suggest it to the board. There are definitely managers in real life that have certain visions or policies, and the board/staff respect it. This carries over to both staff and player signings. Usually, it is determined in real life by how much power is given to the manager vs. the Director of Football, but they at least share ideas or feedback. It doesn't necessarily have to be a permanent thing, but however long the manager stays at the club or wants the policies in place. For example, a lower-tier team may want a domestic policy in place, but as they grow bigger or more successful, they may want to change their policies to reflect that.
Regardless if this suggestion is ever put as a feature or not, they should definitely look at how the club visions/identities behave in the game. For example, you have "Do not sign players over the age of 30", "Sign players under the age of 20", "Sign players of a certain nationality", or "Sign players under the age of 23 for the first team" are all in the game currently, and these types of objectives can be followed manually, yes, but AI staff always appears to ignore these objectives or visions, it seems, half the time. It is possible to be done manually, definitely, but these are people in the FM player base that may not want to deal with transfers, or even at the very least, transfers for youth/reserve/B teams. The same can be applied to staff signings itself.