If we change our opinion on a religious matter for any reason, providing one does not cherry pick and that the opinion is backed up by renowned scholars. Do we have to redo our past acts of worships as we were following another opinion ?

Ustadh AbdulAziz al-Haqqan

No, you do not repeat them. What you did upon a valid scholarly view in a matter of ijtihad is sound and is not redone.