There are a couple ways to do it, But The ChipSwitch is the best way to go with the Hr2600.
You can swap out the CPU that is in the radio, with one from A Lincoln/Hr2510, then it will mod , same as they do.
(cant remember the CPU #s right now)
Thing is you got to have one, so unless you run across a parts radio with a good CPU, you got to buy one.
You can Re-rock the radio by changing X302 (crystal) to shift the radio up/down to the frequency you need.
If you want to do 12 meters, you can swap it out with a 18.000mhz and so on.
The Frequency display on the radio will NOT read new frequency, you have to subtract X Mhz from the display, so if you shift the radio down 4 Mhz, the display will be off by 4 Mhz, not real cool, but if you just want a Radio to get on 12 that will Get-R-Done.
By far the ChipSwitch is the deal, Lots of features that make the radio a lot more user freindly.
L-one might say
BomB Diggity!
73
Jeff
On edit:
I went and looked up some stuff on the 2600........ :?
Info lINKS:
www.radiomods.co.nz/hr2510_hr2600cpupinout.html
www.chipswitch.com/
members.tripod.com/~Malzev/cb-radio/hr2600.htm
www.members.tripod.com/~Rogerbird/