There's two methods to this tutorial.
Method 1. Okay so we all know how to use one proxy on one machine using proxifier, but that affects all runescape clients on the machine not just one.
This tutorial will show you how to use a different proxy for EVERY client you run on your PC.
Okay first of all, make sure you have a proxy for each account you want to run added to proxifier
Next Add a Proxification rule with the following info
Ensure that you set the action to use whichever proxy you want to use for that client
The Important part is the jagexlauncher.exe as this is what will be differentiating your clients.
Next Navigate to your jagexcache directory
..\jagexcache\jagexlauncher\bin
Copy JagexLauncher.exe
Personally I'll rename the new one to JagexLauncher1.exe
You can make as many copies as needed for each proxy you will use.
Ie. JagexLauncher1.exe, JagexLauncher2.exe, JagexLauncher3.exe ...
Now Locate your OldSchool RuneScape shortcut, it should be in a similar path to the following:
C:\Users\...\AppData\Roaming\Microsoft\Windows\Start Menu\Programs
Copy the Shortcut and paste it wherever, I typically keep them on my desktop but you will need to be able to access them.
Rename the Copied one to reflect the jagexlauncher it will open,
ie, I will rename "OldSchool RuneScaoe - Copy" to "OldSchool RuneScape1"
Now Rightclick the new shortcut and click properties
Change "JagexLauncher.exe" to your new launcher name, ie. "JagexLauncher1.exe"
Eg.
Change the Target path from:
..\jagexcache\jagexlauncher\bin\JagexLauncher.exe oldschool
To:
..\jagexcache\jagexlauncher\bin\JagexLauncher1.exe oldschool
Click Apply and then click Ok
Now Return to proxifier and duplicate your original rule for runescape using the clone button
Edit the Copied Rule:
Change the name to your new jagexLauncher name number so you can keep track of it easier
ie, JagexLauncher1 -> Runescape1 etc.
Change the Application from "JagexLauncher.exe" to the new name ie. "JagexLauncher1.exe"
(Additionally you can search for the file using the browse button)
Keep the Target hosts still as *.runescape.*
Change the action to your other proxy
Click Ok on both windows.
And you're done with method 1. Personally, I prefer to rename the desktop shortcuts to their respective accounts so I never get confused on which proxy belongs to which account. Make sure you always do these one at a time so you don't accidentally use the wrong account with the wrong proxy.
Method 2. Right-click the jagex launcher and select the proxy you want through the proxifier dropdown. This is easier, but you run the risk of confusing accounts with proxies.
Any further questions feel free to ask,