If I plug a mono cable into the stereo jack does the guitar still function normally as it would prior to installing the Acousti-Phonic preamp?Updated 3 days ago

Yes. If you turn the acoustic volume down to zero or set the QuickSwitch to Mag, your guitar will play like a regular electric guitar. The only difference is that you need the battery to be good even to run on mag only, as this signal does pass through the Acousti-Phonic for blending purposes.