[Johnngnky]

If i was to use photos again and again with different companies but change the timestamps, will the company know the timestamps have been changed?

What is it a photo of? If it's evidence of a PoD/ broken item/ etc. I'm sure you'll be fine.
Obviously, if it's apparent it's been modified, then they will know.

However, assuming modified well, most companies don't share claim information with other companies (though I know this isn't true of all companies),

I assume OP is referring to EXIF data. In which case, I don't think they can see them as long as OP clears it.