FCxx gets stripped upon loading - meaning that FCxx -> 0L00 replacer cannot work because nothing to replace

I have bumped into some mates who have old songs that use FCxx - and I wrote a FCxx to `0Lxx´ replacer for them, which replaces all of the FCs with 0L. But after telling them about it, they said “Yes, but, upon loading a XRNS with FCxx, the FCxx is destructively stripped out”.

Could this be made to not happen, please?