The option to rearrange existing footprints was added recently (Post-V9 New Features and Development News - #11 by mikebwilliams) - it is in nightlies and will be in v10:
In v9, you can replace your existing footprints with the new array, then resync the PCB with the schematic, using the “re-link by reference” option to link the new footprints to the existing schematic symbols. Remember to turn that option off again when you are done, or it will make undesirable changes to the PCB if you change reference designators in the schematic.
Alternatively, use the array tool to make an array of something else (vias, say), and then snap the footprints on that, before removing the guide items. Or use the grid as mentioned above. Changing grids is a common thing to do, and you can even have presets for each specific use (including a name, and X and Y pitches).