There has got to be a way... I'll play with it and let u know
so i got it to work pretty simple too. and of course you can add any additional variables. such as only do during certain hours and so forth, or if you seriously want it in extreme power saving mode all the time that the screen is off, then its rather simple.
add profile for event, click display, and display off
click new task for this case name it EPSM or what every you'd like
click the + and select action category script, then Run Shell
under command enter this
am start -a android.intent.action.MAIN -n com.htc.htcpowermanager/com.htc.htcpowermanager.extremepowersaver.ExtremePowerSaverConfirmActivity
and check the box for "use Root"
back out ensure you now see a profile for Display Off and its on and the task is set to EPSM and we are all good.
now when every you screen is off the phone will enter extreme power saving mode.
turn screen back on and you will be in EPSM, and just click exit to get out,
a few notee / things to point out, is that you could also add a timer, so that if the display is off, for X amount of time then it triggers the script, or only run between the times of 11 pm - 8 am... the possibilties are endless.
Have fun with this.