RFTools Dimension Editor
With the Dimension Editor you can alter already created dimensions by inserting some types of dimlets. It can be crafted as follows:
This machine allows you to insert some type of dimlets into an existing dimension. Note that the dimlet is lost during this process (you will not get it back even if you deconstruct the dimension tab) and you pay the full power cost for it. There is no way to undo this so be careful. This can only be done with dimlets of type 'special', 'mob', 'effect', 'sky', and 'time'.