I would like to manage creation of different \"theme\" for my site, using LESS.
My idea is to generate different compiled .css files, using each time a specific variable
You need to flip your import directions.
The style.less file should not import any variables.
style.less
Instead, each variableN.less file should import style.less after defining all of its variables. These files will then each compile to a full set of rules based on their variable values.
variableN.less