The virtual directory / web site should allow you to place the new code in a new location, then re-direct all calls to the master web site to the virtual one with the new code. Then if you need to you can re-direct to the old one very easily and quickly. Setting this up depends on the web software, but basically you create a new web site / directory and either change the home folder in the web software or have a re-direct file on the root of the web site to send all requests to the new site without user interaction.
An example might be this code in "default.htm"
I can't help with coding aids, not being a coder as such.