taskkill /f /im rdpclip.exe /fi "username eq %USERNAME%" && rdpclip

To restart it in a .bat:

taskkill /f /im rdpclip.exe /fi "username eq %USERNAME%"
start rdpclip.exe
exit

I would recommend to make it(batch) wait a second between taskkill and start. Without it i faced a problem several times: system had not yet killed the proccess by the time the start command came in. So the new proccess didn't start, and the old got killed. Result: no rdpclip.exe at all =(

cls
taskkill /F /FI "USERNAME eq %username%" /IM rdpclip.exe
ping -n 1 -w 1000 1.1.1.1>nul
start rdpclip.exe

Save as .bat.