if people are still looking to do this (and remove the annoying double notification, if youre runninng handcent or chompsms on behold II), this is how i did it
First you have to gain root access (look that up)
then, get "root explorer" from the market
then, using root explorer go to your system/app and copy your stock TwMms.apk, go back and paste it at a safe location on your sdcard (as a backup)
Then, get the app posted here from emeryfan1988
Modified Mms.apk-Turn-off debug mode, stop application from lagging [Updated: 08/21] - xda-developer...
rename it to TwMms.apk and put it on your sdcard (of course NOT in the same location you pasted the original behold 2 twmms.apk)
Then, use root explorer to go to where you pasted the renamed app, long click on it and hit copy
then, go to system/app and hit paste.. (of course choose to replace the existing app)
This gives you access to all the old settings under messaging, where you can disable the phone sms notification and use just the one from handcent!!
..and behold.. the behold 2 can run handcent with no double notifications and MMS working!!!
if someone needs more detailed instructions, then post and I'll do the work (with link to all processes)