Can 2008 - 2019 Toyota LC200 coil overs be upgraded to a heavier rate coil spring?

No, Icon does not offer a heavier rate coil spring for the 2008 - 2019 LC200. There are other spring manufacturers that make a coil spring of similar dimensions to the ICON coil spring, however the max thread showing would have to be calculated based on the specifications of that coil spring. If more lift is desired the ICON bumps on spacer is recommended over switching to a different coil spring.

51046 - LC200 SERIES BUMP STOP SPACER KIT