A Dremel with a cutoff wheel will make quick work of removing a bit of hardened steel. Cut a little short of where you want the edge to be and you won't have to worry about blueing the blade. That will be quick to grind past.
An old blade of mine that was unusable in a plane was cut and made into a couple of marking knives:I have a couple similar irons stashed, I can't bring myself to throw them away, still dodn't know what to do with them.
Shop Made Knives.jpg
The knife in the center was made from a broken saw blade. The ferrule is a sleeve from a brass compression fitting for 1/4" tubing.
Here is the story on my second marking knife made from a plane blade:
https://sawmillcreek.org/showthread.php?229968
It is my most used marking knife.
jtk