Hi,
Actually, the reason I posted this question is that this information is very hard to find in the user manual.
You would expect to find it in the "Loading community created levels" section, but there is only info on where to copy the files, not how to load them.
To find out how to load them, you have to refer to a parenthesis in the "Tools" subsection of the "Freerider Recharged Level Editor" section, which is not a part of the doc that you read carefully if you are not interested in creating levels by yourself.
You could probably update the "Loading community created levels" to explain how to actually load the custom levels added (it doesn't matter if it's redundant with an information given previously in another section.).
Cheers.