Expanding %1 and other variables from a command

Question

Hi!
I need a simple command to open a specific file (rasphone.pbk) with whatever is the default program for opening text files.
What I have so far:
(Get-ItemProperty -Path 'Registry::HKEY_CLASSES_ROOT\txtfile\shell\open\command').'(Default)'
Which gives me this output:
"C:\Program Files\Sublime Text 2\sublime_text.exe" "%1"
It will be executed for different machines/users. Some may only have the default notepad.exe, others may have different editors.
So I now need to replace the %1 with
%AppData%\Microsoft\Network\Connections\Pbk\rasphone.pbk
while also expanding %AppData%. The default command is
%SystemRoot%\system32\NOTEPAD.EXE %1
where I would need to expand %SystemRoot% as well.
It should be a 1-liner if possible because the command is stored in a database. If I need a script file I have to find a way to distribute that file to each client as well... and for simply opening a file that would be a bit too much.
If it's easy in CMD that would be even better, but I thought Powershell is a capable tool for doing stuff like that in a simple way. I just can't wrap my head around it...
thanks for any help! :)

Answer 1

Use Exanded string to  store variable reference in the registry.
You can do the easily with Regedit. You can export the key and import it on any machine with a click of the file.
Indeed I can replace just the %1 and let the other variables be replaced by cmd.
I actually got it working now without a script file (I really want to avoid using a file). this is the UI I have to work with:
(Remote Desktop Manager)
This is what I use now:
cmd /K powershell -Command "((Get-ItemProperty -Path 'Registry::HKEY_CLASSES_ROOT\txtfile\shell\open\command').'(Default)').replace('%1','%AppData%\Microsoft\Network\Connections\Pbk\rasphone.pbk')" | cmd
It is not pretty... calling cmd to call PowerShell and piping the output back to cmd to execute the command.
I just can't find a way to execute the command including the parameters from a single string in PowerShell.
If you can think of a better way please let me know...
Thanks for the help!