Please call plugins by munin-run.

Some plugins - known as wildcard plugins (like if_ and mysql_) -
can be used with device or other feature by linking them with different
names.
That is why I think you should call plugins via munin-run.

Example:
 UserParameter=munin[*],/usr/sbin/munin-run $1|grep "^$2.value" |cut -d " " -f2

These plugins called by munin-run can read /etc/munin/plugin-conf.d/*.

So I think your script can import more many templates and use them.

Best regards,