Yes, here is one of many tutorials online, they use one program as an example, just substitute with whatever you want to add. Hope it helps.
http://geekswithblogs.net/Solid/archive/2005/09/26/55072.aspx
* Run regedit
* go to HKEY_CLASSES_ROOT\*
* right-click on *, new > key
* name the new key "shell"
* right-click on shell, new > key
* name the new key "Scite"
* right-click on Scite, new > key
* name the new key "Command"
* Click once on Command to select it
* right-click (Default) on right side > Modify
* Add "C:\Program Files\wscite\SciTE.exe %1" to Value Data (don't put the quotes and dont forget to add the %1)
[HKEY_CLASSES_ROOT\*\shell\Scite\Command]
@="c:\\Program Files\\wscite\\SciTE.exe %1"
Now on most files, you can right-click and see "Scite" as option, allowing you to open this file in SciTE.