Extend coax or fibre internally

Hi. I need to relocate my router to another part of the house. The connection, from the existing wall box to the new router position, would be installed by me under floorboards. My service is currently provided by coax cable, but if taking the trouble to install cable under floorboards, then I might be tempted to install a fibre at the same time to the same new location, just for future proofing. I know the length of cable(s) required, but would need them terminated so that I can install at a later date, but have the dB levels adjusted at the same time. I understand that a non-fault engineer visit imay be required. Please can the team confirm whether this can be arranged via the community forum?