Hi Sports lawyer
Did you get anywhere after your post on the 300RR PTB thread we had going a while back
Thanks for the update. I've continued searching for information on an Optional Tuning Kit for the 2016/2017 300RR (or RTL300R) and 4RT260 bikes. But haven't found anything yet that's specific to the 300RR. Have seen some suggestions that the 2016 / 2017 4RT260 3ED/4ED TB/ECU (16400-NN4-L31) is also programmable, but no "I've done it and used this" reports.
Have found that Honda has unified the cable set (38880-N1C-770 UNIT ASSY, SERIAL-USB I/F), and it's used for every other programmable FI bike since MY 2012 that I've found information on -- CBR250R, NSF250R, MSX125, CBR1000RR, CRF450R, CRF250R, and probably more. I suspect this supersedes the 38880-NN4-H00 cable set (first came out for the 2010 Japanese RTL260F), which superseded the 38880-NN4-306 cable set. I have the 38880-NN4-H00 set (use it with the 2010 RTL260F software 38771-NN4-H00) and it appears to be the same as the newer 38880-N1C-770 down to all the connectors and lettering on the switch box.
I'll update with any new information I find. And hopefully Honda will get around to publishing something about the kit.