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Drewwyann said:
I just wanted to know if it was a good idea.

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the blowtorch idea is certainly creative, but that just won't work.  in order to kill a contaminate it needs to be subject to heat for an extended period of time.  you're likely to damage nearly all of the cake trying to bring an isolated area up to temp long enough.  not to mention, contaminates don't just grow on the surface of your jar, if its contaminated near the surface, its likely contaminated on the insides too.  and, its a fire hazard, and a burn hazard.  throw out contaminated projects, start over.  trying to "save" things in this hobby that belong in the trash, nearly ALWAYS results in failure anyway - but with extra time, effort, and materials wasted to boot.

to the original poster, yellow spots are generally bad news.  in some cases, you can have yellowish/brownish discoloration due to metabolytes being released by the mycelium (though when this happens in PF cakes, usually something else is wrong and any time I've seen it resulted in non-fruiting cakes that contaminated once birthed).  sometimes the mycelium will be slightly discolored simply if its in contact with moisture that's condensed inside the jar.

impossible to tell for sure from those pictures though.  perhaps give it a short while longer and see if the spots grow.  give the cakes a smell (be prudent and do so from a distance, or "waft", don't go sniffing the cakes direclty in case it is a bacteria) - anything besides fresh mushroom smell, trash immediately.