I want to update some resource files in a winsxs sub folder. Unfortunately Windows 7 doesn't let me edit these files. Altough I've opened an elevated Windows Explorer I can't seem to be able to grant rights or edit the files. What can I do to get access to these files?

You obviously know what you want to do, so take ownership, viz:Right-click the folder, select Properties > Security Tab > Advanced at the bottom > Owner Tab > Edit > Highlight your username and put a tick in Replace owner on sub containers and Apply > OK. You will only have the Replace owner on subcontainers box for folders not files. Click Yes when you receive the Security pop-up window then click OK to the Close/Reopen message. Make a note of the previous owner in case you want to change it back. Now go back to the Properties > Security Tab. Click Edit > Add. Type in your User Account Name in the box under Enter the objects name to select. Click on Check Names > OK. Click on your User Account Name to highlight it. Check the box for Full Control > Apply and OK etc. You may want to add Take Ownership to the right-click menu http://www.sevenforums.com/tutorials/1911-take-ownership-shortcut.html?filter[2]=Networking%20Internet

Unfortunately this didn't work. Altough I could change the folder's owner and add all rights to the Administrators group I couldn't do this to the files within the folder. So I still couldn't edit these files. Even after setting myself as the owner of one of these files I still couldn't grant rights to myself on them. How is this possible? Can this behaviour be circumvented?

Try using the 'true administrator' account by opening a Run window (Windows key+R), type cmd and press Enter. Now type net user Administrator /active:yes (not the quotes but the 3 spaces) and press Enter. Restart the computer and the Administrator account should show on the Welcome screen. To disable the true account, retype the command but change yes to no.

Splendid! That did the trick! Thanks! I noticed that the /active option is not documented in Windows 7. Is this a (minor) bug or is this a hidden feature?