HI @DEATHFISH,
You don’t need to use custom code instead you can custom activity,and provide the required inputs as shown in the below screen shot.
To install this activity go to package manager in all packages search for set ordinal activity yo will get it.
Another wise you can use invoke method and use setOrdinal method in that and provide the input parameters in parameters field in properties either of the ways should work.
In the target object give datatable.column(index of column you want to move and in parameters give the newindex)
Regards,
ShivaKarthik