You do not have to be rooted in order to go back to .901...
I'll outline how to do this if you are willing to try, it will however clear all your data, so you'd need to resync to get all your contacts and calendar back, and reinstall all of your market apps if it doesn't automatically...it won't clear your SDCard though...
In a nutshell what you'd be doing is to use RSDLite to reprogram your Bionic back to the 5.5.893 OTA, then manually place the .901 OTA on your sdcard and accept it like you would the regular OTAs.
Here's the breakdown of what's needed...
1/ You must have a fully charged battery to ensure you don't run out of power in the middle of the process...
2/ Download RSDLite, Moto drivers, and the .893 FXZ alternative from this thread...
http://www.droidforums.net/forum/mo...-5-893-fxz-901-902-compatible-902-update.html
3/ Install RSDLite on your PC, and install the Moto USB driver for your PC, 32 bit or 64 bit based on what your PC is, (if you already have the driver installed then no need)...
4/ Unzip the .893 FXZ somewhere on your PC that you will remember...
5/ Shut off your Bionic and then reboot into Fastboot by pressing Power and 'Down' Volume at the same time (should say Battery OK, OK to Program, Connect USB Data Cable...)
6/ Connect your Bionic to your PC and launch RSDLite....(your Bionic should now say ..Battery OK, OK to Program, Transfer Mode: USB Connected)...
7/ On the RSDLite screen you should see that it says Fastboot ...USB....Connected, from there you use the tab with the three dots that is next to the Start tab and browse to that FXZ folder, to the NEWVRZ_XT875_5.5.893.XT875.Verizon.en.US_CFC_01 xml file in that folder....Press the Start tab/button, it will go thru several steps, let it finish all it's steps until your Bionic reboots to the Welcome Android setup screen...
8/ Re-setup your Bionic like you did when you first got the phone.... You should now be on stock 5.5.893 and it's radios...
9/ From there download this
.901 OTA zip and place it loose on your SDCard-Ext ...
10/ Now power off your Bionic, then reboot into stock boot menu by pressing the Power button and both the Up and Down Volume keys all together...
11/ When in that Boot menu, press the Volume down button once to get to Recovery, then press Volume Up, it will then come to a screen with an Android guy with an exclamation point, press both Volumes Up and Down together (not power button this time)
12/ You will then be in Stock Recovery, press Volume down to scroll down to the 'apply update from sdcard', press the power key and it will go to your sdcard-ext menu.... from there scroll down to the update901.zip and press the power key....it will then apply the .901 OTA. Upon reboot you will be on the .901 OTA and it's radios...