The best practice is to log the risk and the associated response strategies in the risk register to ensure it is monitored, analyzed, and managed throughout the project. The PMBOK Guide states:
"All identified risks and their planned responses should be recorded in the risk register to facilitate ongoing monitoring and management."
- PMBOK Guide, 6th Edition, Section 11.2.3.1
Ignoring or treating these as mere assumptions could result in unmanaged risks and potential project failure.
References:
PMBOK Guide, 6th Edition, Section 11.2.3.1
Practice Standard for Project Risk Management, PMI, Section 5.3