I see your point, but a strategic change of that sort (announced properly maybe a season in advance) would not only shift the powers, it would change the mechanics to some degree. Changed mechanics also mean that you can "adjust" to them. So if you know that players at the age of 31 -can- become a risk, that would most likely "simply" lead to their trade value shrinking (to be honest, over age 30 it´s almost non-existant already, isn´t it?). So you can either take a gamble (and probably ride an old gun till the bitter end, thus saving some money you don´t have to spend on replacing the guy via TL), or you can look for an replacement when he "crosses the border".
On the other hand - let´s say you have a player for 80-100k in salary age 32, and all of a sudden you lose him to a career ending injury in week 3 or such and he immediately gets off your payroll.
That´s quite a loss for now, that´s true, but even with the money you´re saving for the rest of the season you will most likely have at least "some" financial flexibility to replace him (at least at some point in the season).
The key to it is "planning". If properly announced, everybody can prepare, and make plans.
Zwei Dinge sind unendlich, die Dummheit und das All...