> Someone sent me an early version of substfs.
> Is there an updated version of this?

I did. No, I don't have anything newer.
What you have is what I currently run.

It is still 'unfinished, unpolished'. (see below)

For those who missed my previous post about it, sort of a repost:
What it does? It sits between 'us' and a (remote) file server.
Its purpose is to do substitutions on file names in the 9p messages
to and from the (remote) file server.
Advantage of this approach: no need to adapt the (remote) file servers 
like u9fs), no need to adapt local stuff. Disadvantage: certainly
some performance loss.
Don't know whether the name substfs is correct, or whether something
like substsrv would be better.
For flexibility, to experiment, the substition rules are not built in.
Instead, on its command line it is given the names of two programs that
do back and forth translation. These translation programs just accept
a filename on stdin and output the translation on stdout.

The attached gzipped tar file contains the source and translation
scripts I currently use.

Inspiration and source code taken from multiple places
(u9fs? 9pcon,... see my previous post)

Status:
it still contains memory leaks, which may be one of the reasons for the
machine crash I mentioned in my earlier post of today, subject: Re: PGP)
Also, translation is not yet done for all 9p messages that would need it,
but that is easy enough to add.
Main real problem is that it might loose directory entries,
when reading directories, when translation of directory entry names
extend these such that the result no longer fits in a single 9p message.

Enjoy,
Axel.