I just completed a flight into KEAT in washington state. I haven't used MSFS for about 4 months now, so I'm a little rusty. KEAT has an ILS rwy12 published for it but this approach doesn't exist in RC4 - how do I go about adding approaches such as this ILS rwy 12 in RC4?

You can add an ILS approach to an existing airport with AFCAD 2.21 (for FS9) freeware available in the AVSIM library here. After doing this and insuring the new .bgl file is in a scenery folder included in a libary recognized by the FS scenery library and you have started and stopped FS to cause it to reindex its scenery, you then run the RC scenery update utility.The new ILS will now be recognized by RC and your aircraft avionics raw data instruments such as a localizer/VOR indicator. If you have avionics with a proprietary format database you will need to follow the instructions to add that new ILS. The FS9 default GPS may not see it either.ILSs added with AFCAD will not be seen by FS AI aircraft and they may not land there in IMC conditions. A full scenery utility is required to do this.