Don't confuse MultiStyles with Changing styles. Two different things.

Use the F5 like you have been. Select the bar when you want the change to occur. But keep in mind the changes do not get reflected/updated in the Mixer. So you don't see the changes, you will only hear the changes at the bar you turned them on until you return to original style at a subsequent bar. Not exactly intuitive.

BIAB – 2025, Reaper (current), i7-12700F Processor, 32GB DDR4-3200MHz RAM, 1TB WD Black NVMe SSD, 2TB WDC Blue SSD, 1TB WD Blue, 2 TB SK NVMe, 6 TB External, Motu Audio Express 6x6