Synthetic Oil back to Conventional

[romram]

Got my 2010 yaris service at toyota dealer to have serviced and replaced front brakes ( rotor/pads/shims). eventually had my change oil plus filter and multipoint inspection for 185k Miles
i been using conventional oil since day one (toyota oil @ $ 13.25 ).
for some reason, a NEW asst. service manager wrote in the service card to use SYNTHETIC OIL 0W20. I found it out when i was paying my bills. The price is not the issue thou it cost more @ $44.75.
my concern is, if i can still go back to conventional oil at 190k, since i heard you can't go back to conventional oil once you used synthetic oil, now it will be serviced every 10k and not 5k. In the oil cap recommend SAE 5W-30 ( will it affect any)
any advice? thanks