Both .rfl files and .rns files originate from Reason audio production tools from Propellerhead Software and only this program can probably (if even) convert or somehow export between these two formats. No other third party software that could perform RFL to RNS conversion is known to us.
Convert Reason sound bank to Reason audio project.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert rfl to rns on Windows
Set of software tools for audio production
Convert from rfl file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.