After Installing NotePad++, place the xml file within %AppData%\Notepad++\userDefineLangs, and restart NotePad++.
Files with extensions .cisco, .ios, .xr, .log, and .txt will automatically use this UDL as their default language.
To change this behavior, edit Cisco_IOS_XR_byOsamaAbbas.udl.xml file at the following line, remove txt from ext property, and restart NotePad++.
<UserLang name="Cisco IOS XR" ext="cisco ios xr log txt" udlVersion="1.0">This is an enhanced version of the UDL made by LuisPisco. His UDL can be found here.