Replace text in imported Less file

I am using Less and I'm importing CSS from an external library:

@import '../../../theme.css';

Is there any way to process this imported file in Less and replace some text (like colors)?

I took a look at the replace function, but I didn't find a way to use it on an imported file.

// I am looking for something like this
replace(@importedCss, '#111111', '#555555');