last year i applied for a job that required a school transcript and i submitted my average marks.
this year i changed a few of my grades and applied for the job again. i'm wondering if they'll have saved my transcript pdf from last time and will be able to compare it
Depends on the job. Some employers hold on to applications, especially if you've indicated that you'd like to be considered for other roles. Also if the file this time isn't a PDF, they might get suspicious.
>>17361963
Probably not, but I doubt very much that your grades were what lost you the job.
Aside from colleges, nobody really gives a damn how you did in high school - they just want proof that you graduated.
So changing a few grades isn't likely to improve your chances. Whatever they didn't like about you last year is elsewhere, and probably hasn't changed.