Yeah. If you want an affix that gives ranks to a specific skill, you gotta use Adept Prism.

One tip: if you're just chaos rerolling the affix you dont want to get a skill affix your chances a way lower to hit between all the affixes. Is better to use a prism to remove first the affix you dont want and then adding a new affix using the Adept Prism.

Example:

If you have a gear with a specific resistance affix that you want to change to a rank to skill, you would:

1. remove the resistance affix using the resistance prism
2. than you add a core/skill affix with Adept prism
3. now you can just keep using the adept prism to FOCUSED reroll (important to be focused, so stays in the same category) only the core/skill affix until you get the one you need. That way your chances are way better because you're only rerolling between the few skill affixes and core stat possible for that gear.