It possible to have different versions of Sandvox running on the same computer but preferably not at the same time though it is possible. You may want to do this if you are trying out the latest beta as well as having the current release version.
I rename the release version Sandvox-161 and the beta Sandvox-beta and keep them in my Applications folder. Be careful when opening the Site Documents because by default they will open in the beta.
I find it easier to launch the Sandvox version I want to use then open the Site Document I want to work with from within Sandvox.
I first started doing this when moving from version 1.2.x to 1.5.x of Sandvox, There were major changes in the site document format between versions 1.2 and 1.5. Sites created with 1.5 are not compatible with 1.2 and 1.2 site don't always look or work the same in Sandvox 1.5.
You can keep version 1.2.x and rename it then download Sandvox 1.5.x from the Karelia site.
When Sandvox 1.5.x opens a 1.2.x version site document, a site document called 'sitename-previous' is created. This 'previous' site document is the 1.2.x Sandvox created site document.
To open the 'sitename-previous' site document you need Sandvox 1.2.x on your system. I have renamed the Sandvox 1.2.8 application to Sandvox-old and keep this with the latest version of Sandvox both in the Applications folder. This way, it is possible to open both versions of Sandvox and their corresponding versions of the site documents.
Be careful to open a 1.2 site document with Sandvox 1.2.x. If you open 'sitename-previous' with Sandvox 1.5, the site document will be converted again. This will create a 'sitename-previous-previous' i.e. original site document and the 'sitename-previous' becomes a 1.5.x site document. Very confusing.
A way to avoid this is to right-click on a 1.2.x site document and choose Open With: and select the old version of Sandvox.
Open With: can also be set from the Finder: File > Get Info dialog.
Although I found that if Sandvox 1.5.x is open and I double-clicked a Sandvox 1.2.x Site Document with the Open With adjusted, it would be opened and converted by Sandvox 1.5.x regardless of the Open With: setting.
If Sandvox 1.5.x was closed this same file would open in Sandvox 1.2.x when double-clicked. So opening by right-click > Open With is a good idea.
When working with both versions of Sandvox at the same time to make comparisons of the site document conversion, I found it easier to get in the haabit of using the Sandvox: File > Open... menu option from the relevant version of Sandvox. Sandvox 1.2.x refuses to open a 1.5.x site document file.