Question about advancing a templated creature

[Lej]

Hi, I have a question about templates and adding HD:s/Class Levels.

Let's say I add the Fiendish template to an Annis. The Annis has CR 6.

Since the Annis has 7 HD the resulting Fiendish Annis gains, among other things, +1 CR and Resist Fire 5 from the template. The Fiendish Annis has CR 7.

a) If I add 1 level of Fighter to the Fiendish Annis what will the CR be? Does the added level retroactively increase the CR gained from the Fiendish template resulting in CR 9 (Annis 6 + Fiendish 2 + Fighter 1) or simply further increase the CR by +1 resulting in CR 8 (Annis 6 + Fiendish 1 + Fighter 1).

b) Does the added level of fighter increase the Resist Fire from the Fiendish template to 10?

c) Questions a) and b) but instead of adding a level of Fighter simply increasing the HD by 1.

tl;dr Does adding HD/Class Levels retroactively increase the CR change and/or bonuses from a template?

An answer with references to rules would be preferred, but anything is more than welcome! Thanks in advance.

[kitep]

It has to be a fiendish Annis before it can be a fiendish Annis/fighter 1, so I would say the CR is not retroactive, ie CR 8.

The fire resistance would come off the final HD, so fire resist 10.

[Lej]

It has to be a fiendish Annis before it can be a fiendish Annis/fighter 1, so I would say the CR is not retroactive, ie CR 8.

The fire resistance would come off the final HD, so fire resist 10.

Not the answer I would have expected. I would have assumed either CR 8 and Fire Resist 5 or CR 9 and Fire Resist 10. Seems a bit dangerous to have its fighting power increase but not CR.

[Halinn]

Aside from the fact that the Fiendish template is way overpriced, both in CR and LA, it would be CR 9, unless you don't count class levels as HD with regards to the template (although I have only seen that argued for the Feral template, that specified granting special attacks based on monster Hit Dice [though the granted special qualities don't have that qualifier]).
Adding another racial hit dice would, no doubt about it, raise CR to 9 with the corresponding fire resist increase.