Well, now we're showing my general lack of familiarity with the KE06 in particular. But downloading the manual MKE06P80M48SF0RM.pdf, section 10.2.1 details which 'alternate zero thru seven' will select for a pin, the first paragraph of which has this statement:
The Port Control Module is responsible for selecting which ALT functionality is available on each pin.
I assumed that was TRUE, and hence my prior suggestions.
That being said, I SEE YOUR POINT -- chapter 11, Port Control, makes NO mention of such Port Control Registers (as I use in the 'K' family).
It appears that for this family SOME control is REALLY in the SIM_PINSELx registers (12.2.4&5). But I'm afraid I have to agree with you on this one! It is NOT obvious how this works. In the table on page 141, PTB1 can serve as PTB1, KB0_P9, UART0_TX, and ADC0_SE5 (default). So I can see how UART0PS can move UART0 'away' from PortB (although i DON'T see how you keep UART0 from taking ANY I/O pins, maybe if it is not 'clock enabled'?), but that can't POSSIBLY be the whole story!
SO, I have to 'bow out' on being ANY HELP AT ALL (SORRY!), and we need to find someone more familiar with KE to help!