in my opinion

[olgatwo]

Can I say "In my modest opinion" instead of "In my humble opinion"
and if so, would it have any other shade of meaning?

[Raymott]

Can I say "In my modest opinion" instead of "In my humble opinion"
and if so, would it have any other shade of meaning?

Yes you can. They mean pretty much the same thing, and are just as often used ironically as literally.