Is it permissible to sometimes adopt the more cautious opinion and at other times the less strict opinion on the same recurring issue, knowing that the opinion of the more authoritative scholar might contradict the more cautious opinion?

Acting stringently (taking the more cautious approach) is supererogatory, not obligatory. So, if you act upon it sometimes, you have done well. And if you refrain from acting upon it at other times, following a trustworthy scholar, there is no sin upon you. This is not blameworthy 'talfiq' (piecemeal combining of different juristic opinions).