I did something similar with my Harman, I was not able to find the actual bulletin either, but it was easy to figure out.
I'm on the road for work right now, I'll see if I can get my wife to take some pictures and I'll put them up.
Meanwhile, I'll try and offer some insight.
The first post on this
https://www.hearth.com/talk/threads/7790/ thread has the specifics that you need to consider.
First off, yes, the stove will re-ignite when the t-stat calls, which will take care of the 4-blink.
HOWEVER... Your success with this modification will vary on how you intend on using the stove.
Using a digital, set-back t-stat as it is intended on being used may not offer the result you are looking for.
To begin with (most of this I'm sure you know), using the room temp sensor requires the stove to be run in Room Temp mode, for which the thermostat is set on the stove computer board. The room temp sensor and stoves computer do a very effective job at maintaining a constant room temp, assuming proper placement of the sensor. (Despite your dealer/installers recommendation, hanging off the back of the stove is NOT a good place for it, there are too many variables in play; simply moving the sensor 3 feet away will greatly improve the stoves performance in Room Temp mode. )
Since the Harman t-stat is internal and dependent on the input of the room sensing probe, all we are able to do in interrupt the signal, causing the stove to believe that the sensor is unplugged and go into shutdown (4-blink).
If you intend on using it as a real set-back t-stat where at one time, you want the room at, say, 65 and then at another time you want it to increase the temp to 80 and back again, we need to look at what is happening with the stove, the igniter and the t-stat. First, for the room sensing probe circuit to be active, the stove needs to be in room temp mode. The temp on the stove "Room Temp" dial should be set to the highest of the temperatures in play, for this case, 80. When the t-stat allows the stove to burn, regardless of what temp the t-stat is set at the stove is going to try and get the room to 80. To actually achieve this effectively, the t-stat should be set to its MAX setting (usually 90). At this point, it is allowing the stoves computer to be in control. The roll-back (65) set on the t-stat is when it is going to get interesting. If the igniter is in Auto when the t-stat rolls back, the stove will go into 4-blink and shut down until the t-stat calls again, at which point the stove will re-start, re-ignite and burn, trying to get the room to 80, until the room reaches 65, satisfies the t-stat, breaks the circuit and puts the stove back into 4-blink. Now I don;t know about your house, but in may house, that would be a lot of starts and stops. If the igniter is in manual mode and the t-stat rolls back, the stove will go to min burn, until the t-stat calls again. If you are going to burn 24/7, this is probably the mode for you.
To answer the rest of your questions, you can simply cut the supplied probe wire and splice in up to 50 feet of regular 2-strand thermostat wire. They seem to recommend 24ga, though I am using the larger 18ga with no problems. The probe should have come with your stove and is a 6' piece of wire with a coated tip on the end, it just plugs into the back of the stove.
Just remember in all of this, you are running the set-back t-stat IN SERIES with the room sensing probe and the probe still needs to be present in the circuit for this to be effective. What this means is that you are going to have to wire the t-stat in kind of an abnormal manner. Using the Rh and W terminals, you will use the red wire from the thermostat wire AND the red wire from what is left on the probe. I don't think it matters which one goes where, it is simply breaking the circuit. The other wires (usually white or black) get tied together to complete the circuit.
This will probably make more sense with Pics, but the wife is in bed, so they will have to wait till tomorrow. FWIW, I run my set-back t-stat as a timer, it turns the stove on before the wife comes home from work and shuts it off before she goes to bed. It is always set on 75 and does a great job.