Identify the rail you mean
The opener rail connects a ceiling-mounted operator to its moving trolley; it is different from the door tracks along the sides of the opening. A question about reusing one does not answer whether the other is suitable. Provide both old and proposed opener model numbers when discussing the installation, plus the door height and any nonstandard mounting arrangement.
Use the manufacturer’s compatibility decision
Chamberlain Group recommends replacement of the entire opener rather than assuming existing rails and parts are reusable because the new motor looks similar. Ask the installer to explain what the quoted package includes and what manufacturer instructions support any retained component. A used rail’s apparent straightness or matching bolt pattern is not enough to approve an installation.
Compare complete costs and functions
A low motor-only price may exclude drive components, controls, sensors or setup that another proposal includes. Put those differences beside the total rather than comparing the motor names alone. The new opener also needs a suitable mechanical door; correcting worn springs or damaged track is separate work and should be identified before the operator is expected to move it.
Your questions
Are the door tracks replaced whenever an opener changes?
Not automatically. They belong to the door assembly and require a separate condition and compatibility assessment.
Can I decide by matching the rail length?
Length is only one characteristic. Use the exact product instructions and supported configuration for the replacement.