If the remote system is at all usable, you may be able to overlay a new userland while it is running. But this is tricky business if you don't really understand all the details. So I'd recommend:
make an image copy of the remote system on a local system and practice read and throroughly understand the scripts is pkgsrc/sysutils/etcmanage (and also sysupdate which is similar in intent but different) find a hosting place that will let you boot a cd image/etc. your situation does not sound robust
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