Necromancers and templates

[paranoidbox]

Ugh, I give up. Either I simply can't understand this or I can't find what I'm looking for.

How do you, as a necromancer, add templates to your undead? For instance, you want to make Fiery Skeletons... how do you do this? Is this simply done via Animate Dead and you account for the extra fractions of HD that the skeletons cost? Or do you need Create Undead for this? Or is it done by DM fiat?

[OldTrees1]

In general, you don't unless your DM uses DM fiat (having templated undead cost extra HD is a good system).

However there are some specific examples that you can. For instance you can Spellstich an undead by paying the gp cost of the template. Likewise you can add Evolved Undead by having that undead live long enough.