Manually install a shared LPX gui (general user interface) theme
1) Right-click Logic X application > show package contents.
2) Navigate to the Logic X folder called “A”, which is here:
Logic X Pro
3) Make a back-up. Inside “A” there is a folder called “Resources”. Option-drag this to the desktop to make a back-up copy. Make sure you’ve made a copy of this folder containing the standard gui resources and not just an alias. IT MIGHT BE A GOOD IDEA TO “COMPRESS” (ZIP) THE WHOLE LOGIC APP FIRST in case you accidentally mess with wrong folders.
Edit: Also, I suggest “duplicating” the Logic app (right-click it and choose “duplicate”) & using Time Machine just before you try to do anything… YOU HAVE BEEN WARNED.
4) Rename this folder something other than Resources (e.g. “Logic Default Resources 10.x.x” or “Standard Resources 10.x.x”).
5) Download the gui file from the link.[*] Once downloaded, unzip the file. This will give you either
a) a new folder called “Resources” or “Resources_for_the_most_brilliant_theme” or something like that, including both the changed and unchanged files, all together appr. 90 MB of stuff; or
b) a folder (perhaps also called “Resources”) with tif image files and a plist-file, about 3-9 MB of stuff.
Nowadays almost all of the modifiers use option b! (That is, usually you must follow 5b and 6b.)
6) Now simply drag
a) the new Resources folder into the Logic folder called “A”, or
b) the new tifs and plist to the default Resources folder. You will be asked whether you want to “replace” > yes you do.
7) Restart Logic to use the new gui.
If you want to go back to the old theme, just re-name your back-up copy of the default theme “Resources” and drag it into the “A” folder.
PLEASE NOTE that most of the themes are non-Retina. Retina tifs have the post-fix “@2x”. If those have been changed as well, the theme can be used in computers with Retina displays.
EDIT: There is now a video instruction made by Paul Yarrow: http://www.logic-cafe.com/lc/index.php/on-test-custom-themes-for-logic-pro-x
Around 4 minutes you also see how you should NOT do it in the case 5b where only the modded files are included in the download. As he notes as well… 🙂 The right way to do it is there at seven minutes.
Original instructions were modified from the ones given by Lee Wilson at Gearslutz: http://www.gearslutz.com/board/logic-pro-x/857146-custom-logic-x-guis-thread.html