It is possible via a work around to 'replace' activities or blocks in a published template. It is always possible to add activities and blocks to a published template:Create a new activity and make sure everything is set up as desired.Next publish the new activity in the template by clicking on the globe icon ( ) or when editing the activity by clicking on Publish. Select the course(s) in which you want to activate the activity.You can now hide the 'wrong' activity by clicking the eye icon ().  In the popup choose whether you also want to hide the activity in the existing course(s).The old activity is now no longer visible for the learners. This also means that the progress on the old activity is no longer visible for them.You can also copy the whole template and make the changes there. This template will be published separately and so will be the new courses created to this template.