If the file is already in the database, there are a few ways to trick it however the key here is to know if the motor designation has multiple entries. The top of the sheet (if there are multiple entries) will have an active dropdown arrow on the rhs of the motor designation field. For example, you will see that there is more than one entry for motors like the AT F50 and F62. If the motor you are interested in only has a single entry in the drop-down, add the .eng version of the file... then what you do is you append to the file name "_1" just in front of the .eng.
Evidently the multi-entry drop down is enabled via the .eng files (afaict the rse files won't do the same but I have not tried it.) If there are already multi entries, then you would likely add _2 .engor _3.eng etc. (so these examples would be: AeroTech_F50_2.eng... I wanted a new G77 thrustcurve and found I had to add it as AeroTech_G77_2.eng because the current one already had two entries!) IF i had I examined what is in the OR source and found out how this "works". IOW if you see two items in the drop-down you'd use _2 for your new file of an existing entry. If the dropdown is inactive (i.e. only ONE entry) you use _1....
So If you have an updated thrust curve you can add it to the stable by determining what _N.eng to use.
BTW I've managed to figure out how to strip out the engine list in OR without recompiling the code and have all the curves as files... Anyone interested?