How to apply a skin at page level?

This is currently not possible at page level (see Skin Levels)

However here's a workaround:

In XWiki Syntax 2.0:

{{velocity}}
#if("$!request.skin" != "XWiki.YourSkin")
$response.sendRedirect($doc.getURL("view", "skin=XWiki.YourSkin"))
#end
{{/velocity}}

In XWiki Syntax 1.0:

#if("$!request.skin" != "XWiki.YourSkin")
$response.sendRedirect($doc.getURL("view", "skin=XWiki.YourSkin"))
#end