The SPWebConfigModification class is used by features to make changes to web.config which need to be applied to all web front ends in the WSS farm. These modifications are 'remembered' by WSS and this allows WSS to remove them when they are no longer required.
Sometimes it is desirable to make modifications to web.config without having to write a feature. If you want to see the stack trace when you get 'An unexpected error has occured' or if you want to add or change an existing 'appSetting' entry, it would be useful to be able to quickly do this via the browser.
To this end I have written a web.config modification manager. This shows the current modifications and allows you to delete them. It also allows you to add new entries which inserts new elements or changes the attributes of exiting ones.
Using this allows you to add changes to web.config on all servers within a farm.
The page also gives examples to assist you in creating the right entries...
The page does have validation to ensure you do not add incorrect entries, which can
lead to problems. If you find that you cannot add an entry, which you believe to be valid you can disable the validation by adding
?novalidation=1 to the query string.
There are two options for installation. The first is simply to copy the aspx page (webconfig.aspx) to the ADMIN folder. You can then access the page by going to /_admin/webconfig.aspx from central administration.
The second is to use the installer which will add the webconfig.aspx to the ADMIN folder and also add a link to the 'Application Management' tab in central administration.
Download the aspx page only
Download the solution setup
Once again I will say thank you to Lars Fastrup for providing the solution installer.
UPDATE: You can find an updated version at Harmjan Greving blog.