Q:

Running Minecraft from a backup folder

I have several backups of my Minecraft folder, all inside my roaming folder, named (in order) MinecraftOld1 MinecraftOld2 and so on. However, you are unable to rename a folder to .minecraft (or .anythinghere for that matter too), so how can I replace my .minecraft folder with one of my backups? Copying/pasting is not an option owing to the size of the backups I make (it will take around an hour to move it into the new folder, and surely there must be a quicker way to just rename the folder?)
Any alternatives that allow me to run the game from this backup folder are also welcomed.

A:

You can use the Command Prompt to rename folders and files with otherwise "illegal" characters.  It's a fairly simple process, though it may seem scary since it's the command prompt.  

Open a Command Prompt (search "cmd" in the Windows Search bar)
Change to the directory that contains the folder you wish to rename.  To do this, you will need to use the cd command (change directory).  If you don't want to type out the full path of the folder, open a File Explorer, and navigate to the folder that contains the file/folder you wish to rename.  Then, type cd (with a space) into the command prompt instance, and then click and drag the folder from the File Explorer instance into the command prompt.  This will automatically put the path into the command prompt for you. Otherwise, type out the path exactly as it is.
Press enter.  Your current directory should now be changed.
Type rename <"original folder name"> <"new folder name"> (don't include the < or >).  In this case, for your <"new folder name">, you will want .minecraft.  Note that the double quotes are only necessary if spaces are in the folder/file name.  You can omit them otherwise.
Press enter, and your folder should be renamed! 

Here is a picture of my example doing this, as well as an additional source that explains the above steps:

