Can I replace my furnace's high limit switch with a comparable third-party part?
I have replaced over temp switches in the past because the one that failed was no longer made.
I used a slightly low temp rating as the exact temp was not available. Most over temp switches are manual reset. 
This is a safety so if there is something wrong you have to reset it by pressing a small button on the switch.
Don’t replace with an automatic reset because this can damage the fire box and possibly start a fire.