actually Pluto overwrites network settings with those stored in mysql tables on every system boot.
I can suggest a very simple (and not really elegant) workaround that I used to modify network settings.
I created a modified interfaces file, naming it interfaces.mod. In this file I put my own network settings.
Then I edited the script /usr/pluto/bin/Network_Setup.sh , located where it gets network config from mysql, and just before the line where network services are reactivated I added a simple line:
cp /etc/network/interfaces.mod /etc/network/interfaces
In this way I overwrite the freshly extracted network settings with my own ones.
Althoug not really elegant, this workaroud works fine.
The only drawback is that when a Pluto update occours you may have to re-add that simple line to your Network_Setup.sh, as the update process may replace existing scripts with new ones.