Is it possible to split an activity? No, this is not possible, but there are two options in configuring something similar in Merlin Project.
Following steps allow you setup reoccurring tasks in Merlin Project.
Create first one activity within you can manually insert children activities.
By a given start date, you can schedule individual activities and distribute them within the activity group. In case they always occur after a fixed amount of time, link them to each other and select all dependency lines. Now you can enter the amount of time as Lead.
Expand or collapse the group as desired.
Another option to record reoccurring tasks in Merlin Project would be to use events. Select an activity and call the "Insert" menu. Select therefrom "Attachment > Event".
In the Details (the secondary project view) you can schedule the individual events and insert new as desired.