No. The profile population mode is locked as soon as a Jira admin confirms it.
The only way to switch is to uninstall Meridian People & Skills Hub and install it again, then choose the other mode. Assume that the skills, suggestions, and blocked skills collected so far are gone, and that the app starts over with a fresh scan of the last 30 days.
The app states this twice before it saves, in a warning on the admin page and in the confirmation dialog, where the button reads Confirm & lock.
Why the decision is permanent
The two modes treat consent differently. In Strict Compliance every skill on a profile was accepted by the person it belongs to. In Maximum Velocity the app writes skills without asking. Switching from Maximum Velocity to Strict Compliance afterwards would leave a profile full of entries nobody confirmed, and switching the other way would silently turn open suggestions into published skills. Locking the mode keeps the data consistent with the promise made when it was collected.
What happens to the data on uninstall
Uninstalling removes the app's data. Reinstalling starts from an empty state, so the earlier skills, suggestions, and blocked skills do not come back on their own. Recovering them is only possible through an Atlassian support ticket, and only for a limited time: Atlassian finally removes an uninstalled app's data after 30 days, after which it cannot be restored. Treat a change of mode as a fresh start, not as a way to keep the data you already collected.
What to do before you decide
Read Choose a profile population mode, which compares the two options, and involve whoever owns data protection questions in your organization.