Conversion binary with unused byte at 0xFF

[IlConte]

There is the possibility to convert in binary mode with unused byte at 0xFF instead 0x00 ?

[Tesla DeLorean]

There are also tools like srecord if you can pass/control what goes on the command line

https://srecord.sourceforge.net/

Don't tend to use, but suspect objcopy has options for empty/slack bytes, and ones own processing tools could also be made aware. On some STM32 parts the erased/blank state is 0x00