Let me try to coble some thoughts together on infiltrators and Cavaliers. This will be limited based on my knowledge of the classes.
Infiltrators:
o start with, my understanding that the shift from ninja invisibility to plausible dependability has already taken some of the bite out of this class. Additionally I have heard it constantly said that gaining the class does not really allow much by itself and that the real challenge is getting one's swordsmanship and infiltration skills up and that takes time and money and is already a progression path by itself. In fact, I am willing to bet that many players are frustrated that, after having worked so hard to meet H/P requirements, they find that they have really gained little and must now start on the equally steep path of skills training.
In short, I am not sure that much extra needs to be done with the infiltrator aside from your chance of getting caught is lessened with high H/P and increased by low H/P. All part of the plausible dependability thing.
Cavaliers:
This is a class that I think really should benifit for having a high H/P and suffer for having low H/P. To start with, I would not change the H/P requirements for unit size and troop types. This means a character who immediately changes to Cavalier still can not recruit cavalry and still haves to deal with the classes restrictions. I would set a H/P baseline (probably the current requirement so 20P/50H or something better) If you have around that much H/P you gain the increase to the number of Cavalry or SF you can recruit. If you have half that, you get half the increase and so on.
This means a brand new 1P/8H character that switches to Cavalier will not see much mechanical benefit. They might gain in jousting during combat instead of swordsmanship, they have an excuse to not perform certain acts and have the right to RP their characters as they see fit from the beginning on.
I will also add that it is still possible to place a restriction preventing characters of players whose accounts are less that X days from changing classes if the dev team feels there really is value here. It might also be cool if old player with new accounts could opt out of the newbie protection benefits in exchange for losing any new account hindrances..