you can always switch back to any windows mobile ROM by flashing the official or a custom windows mobile ROM just like when you had windows mobile using the Official Sony Ericsson ROM Update utility or SD Card KOVSIMG method as the SPL or windows mobile bootloader will not be effected

There has been few reports on the battery meter not showing the correct percentage of battery or random screen flashes when the device start even when you shift back to windows mobile but a proper ROM formatting should take care of this problem and this is a vary rare case

Sony Ericsson Xperia X1 Windows Mobile 6.5 ((INSTALL)) Download