It is necessary to automatically change the last 1 byte of a bunch of files. How and what?

Question

hex

In general, roughly speaking, there are a couple of thousand files, in each of them change one byte, the last one, for example, mb is there some kind of software, or any ideas how to do this?

Answer 1

Here it is:
FILE *f = fopen( fname, "a+" );
fseek( f, -1, SEEK_END );
byte b = 123;
fwrite(f, b, 1);
fclose(f);
Why change the last byte? What is the end goal? What algorithm to change?