Update last-modified-date, if I want

Hi,
my situtation:

I want to order my posts in the loop with the last-modified-date DESC.

Thats no problem.
But I want that not every edit modify the last-modified-date.
This is required, for example, if I change just a word.

I think it would be great if there is a dialog after I clicked on “Save” or there is a meta box with a checkbox “do you want to set the modified-date?”

I hope you understand what I mean.
My English is no the best. But I hope you unterstood me ??