"Frequencies at will" isn't quite what I'd call it. ?
At least, not for GMRS usage. Scanner usage on other bands/services may be somewhat "at will" but will still be from FCC listed frequencies (except for Amateur, and maybe the AM Aircraft bands, all services use FCC defined frequencies -- Amateur is granted a frequency range, and may use any ad-hoc frequency within that range -- channelization is by Amateur convention in the VHF/UHF bands and even that is not constant [some regions use 25kHz spacing on 2m, others use 20kHz spacing to fit in more "channels"])
Basically -- don't bother changing frequencies for the factory pre-set channels. For radios that permit adding "channels" basically copy the nearest matching pre-set and then modify tones/power level/name as needed. For the Portland repeater, that would be copy the .550 repeater channel (#23 in most linear schemes) to an empty slot, change the name, set Tx/Rx CTCSS tones to 100.0, ensure wide FM, give it a default power level (High, most likely). Done!
For general scanning (Weather if not built-in, for example), the critical items are the Rx frequency and bandwidth (25/20/12.5kHz), though setting Tx to match Rx may reduce confusion. Tones should be NONE, power should be irrelevant as the unit should not be trying to transmit on these (if there is a Tx Inhibit option, for safety, select it on the channel). Most Land Mobile is on 12.5kHz these days; Amateur (and Weather) are still 25kHz I believe. MURS 1-3 are 12.5kHz, 4&5 are nominally 20kHz [25kHz is safe] but 12.5kHz is allowed.
