New wiki in a group changed other existing wiki's in the group

Question

We created a new wiki page for a group under manage site -> Applications -> Add Application. After completing this new wiki, we noticed that existing wiki page applications also changed to the edits done for the new application. Why did this happen and how can we retrieve the original design of the other existing wikis. 
 New wiki: PowerPoint templates 
 Old wiki that changed to look like new wiki: Mentorship program

Former Member · Accepted Answer

When you say "edited the wiki template" - I'm guessing you edited the page via Manage > Edit Group Theme > Edit this Page? In that case, the page edits apply to all similar pages within the Group - note that you are editing the Group Theme, not the Wiki theme. 
 A few options for you: 
 
 For your powerpoint template use case, you might look at using a Media Gallery instead of a Wiki to house these. Media Gallery page changes won't cross with Wiki page changes. 
 You could create a separate group, as group is the most granular level of theme control you have when adjusting theme for Wiki pages. 
 If you are interested in customizing further, you can look at the Developer Training for Themes , specifically implementing IThemeableApplicationType for Wikis. 
 Community version 12.0 introduced Articles, which are separately themeable out-of-the-box. If you are able I would recommend upgrading and converting your Wiki usage to Articles.