Since you want to take the repair part from 7500 to 40000, use the speedo-square-drive end of the old cable and a drill to roll it forward. Opening the security-press-fit housing can be done but takes a lot of care and patience and meticulous work to not accidentally destroy the speedo.
Also check your state's Motor Vehicle Department web site for the form you will need to disclose that the odometer was replaced and has been adjusted to read actual mileage, or does not display actual mileage and title will forever after have NOT ACTUAL MILEAGE, or if your state exempts 10+ year old titled vehicles from having accurate odometer statement (varies by state).
Most states take consumer fraud by false odometer readings very seriously so that "Failure To Comply" with the rules is taken as prima facie of guilt of attempted fraud.
2009 Honda Rebel 250 "The bravest thing for me to do is admit when I am wrong" - unknown HRF Answer #1 You should take the MSF Rider Course HRF Answer #2 You need to clean your carburetor HRF Answer #3 Sorry we assumed if you didn't say otherwise