Well creating a large number of period mapping from 2013 to 2015 will take a while to create manually. Creating the same period mapping for multiple application is also a trouble if you create It manually.
If you want to edit the Period mapping under Global mapping
You need to extract the it under Application -> FDM Enterprise Edition -> Global Setup Artifacts -> Period Mapping
The Extract of the period mapping from LCM would like below,
Use the same format and append all the needed period and get it imported it back
If you want to edit the Period mapping under Application Mapping
The process remains the same, but the LCM export needs to be taken from Application data and from the name of the application you actually want to add the period mappings
Hope this was useful, happy days with Cloud!!!