User blog comment:FairyRaven/Fairy Tail Chapter 375: The Supernatural, Review and Commentary/@comment-7418318-20140314102909/@comment-24066070-20140314110535

He did use Precht's chain magic in one panel if I saw it correctly.

You do raise an interesting point when discussing how much he can use. I think you're right when you say he can only use what he absorbed. To think even further, I wonder how much he can use of Precht's magic.

Since Demons use Curses rather than Magic, it may be the case that Fran won't "naturally" recover the soul's magic he used and perhaps the soul itself can't recover the magic while it's dormant inside Fran. This could mean he's limited to the amount Precht had at the moment he was absorbed by Fran and then he may need to think twice before casting spells like Amaterasu or Grimoire Law.

It's also possible that Precht's soul would become useless after Face goes off.