Simply create a new "Temporary" page in BV with some announcement like "Temporarily Offline For Maintenence" and publish it as
index (being sure to
first Save your current
index page as something else so you can re-publish it later without it being overwritten by your 'placeholder' page --
like indexOrig).
* Be sure to complete all the Page Properties (Page Title, etc.) and a toned-down METADATA (Author, very short KeyWords - limited mostly to Page Title words as page content will be unsupportive, Page Description) so you 'protect' your already cached SE values best you can ..... EXAMPLE
That's the simplest .... another method is to use Blue FTP Manager tool in BV to delete the
index.html page file (effectively rendering your site useless, and possibly endangering any SE values previously earned). Once you are finished doing whatever you are doing, simply re-publish your unchanged
index page.