I'm not very experienced with Swiss, but you can region change using modmii after first ensuring your softmods are up to date by running the main Modmii Wizard or its syscheck updater wizard
Any region changer modmii edition may allow u to change just the video mode without fully region changing, but be very careful manually tinkering with the settings of this app.
You can also adjust the video mode settings with a custom bootmii.ini config file (u can build this with modmii) set to autoboot the system menu or whatever. And if u don't have bootmii boot2 u could configure priiloader to launch bootmii ios, which in turn will autoboot the system menu or whatever with your selected video mode as specified in bootmii.ini. I'd start with this, it's the least work and least risk, if it doesn't work to your requirements then try the other methods