mach_inject or Simbl for inject code into the Finder

Question

I made a Simbl plugin that inject code into the Finder. And it works well but at every restart I must relaunch the Finder to allow my code to properly inject itself.

So i made this LaunchAgent :

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>com.overlay.launcher</string>
    <key>KeepAlive</key>
    <false/>
    <key>RunAtLoad</key>
    <true/>
    <key>ProgramArguments</key>
    <array>
            <string>/bin/bash</string>
                    <string>-c</string>
                            <string>killall Finder; open /System/Library/CoreServices/Finder.app</string>
                            </array>
</dict>
</plist>

My plugin just display an Overlay or badging on files.

Is there a better method ?

Since three days I try to use mach_inject but it's a bit more complicated, and i don't understand how to make that my plugin to properly inject into the Finder . My plugin is in objective C and I used the swizzle method to override the method in the Finder, is it possible to do this with mach_inject ?