I think those scripts should be executed before the restoration of mydata.tar.gz, cause the user personalization should be more important that the extensions decisions.
For example, I made a partial translation of tc and so I also translated the jwm menu. Because the user can be different from the default tc I created the following script in the tce.installed:
#!/bin/sh
mv /tmp/.jwmrc_ita /home/$USER/.jwmrc
but this overrides my jwm menu, that is different from the default one (which is in english), but also from the one provided by my translation, cause I have some lines at the bottom of .jwmrc:
......[<StartupCommand>sudo getTime.sh</StartupCommand>
<StartupCommand>mixer.sh</StartupCommand>
<StartupCommand>xonclock</StartupCommand>
<StartupCommand>conky -b</StartupCommand>
<StartupCommand>xmodmap -e "clear Mod4" -e "add Mod5 = Mode_switch"</StartupCommand>
</JWM>/code]