Yes, the travel of the 2021-2023 SID SL C1 can be changed to 80mm or 100mm by replacing the air shaft. 110mm is not possible for the C1 generation of SID SL.
11.4018.111.009 FORK SPRING DEBONAIR SHAFT - (INCLUDES AIR SHAFT AND BUMPERS) 80MM-29 (32MM) - SID SL C1 (2021-2022)
11.4018.111.010 FORK SPRING DEBONAIR SHAFT - (INCLUDES AIR SHAFT AND BUMPERS) 100MM-29 (32MM) - SID SL C1 (2021-2022
RockShox service kits and spare parts are best obtained through your local shop or dealer. See our dealer locator, below, to find a dealer near you. If no one is currently listed near you, then please search for local shops via your preferred web browser.
https://www.sram.com/en/dealer-locator
Manuals and additional information about RockShox and SRAM components can be found at our service site, linked below.
https://www.sram.com/en/service
Further questions?
Reach out to Rider Support by Asking A Question at the link below.
https://www.sram.com/en/rockshox/campaigns/rockshox-rider-support