Target SharePoint layouts pages with CSS

/* This will find MyID and hide it only on layouts pages */
form[action^='/_layouts/'] #MyID{
 display:none;
}

SPList.NeedUpdateSiteClientTag property

SPList.NeedUpdateSiteClientTag  is a boolean value that determines whether to editing documents in this list should increment the ClientTag for the site. The tag is used to allow clients to cache JS/CSS/resources that are retrieved from the Content DB, including custom CSR templates


When an item in this list is modified, the application file cache version for the site that contains this list MUST be updated.

MSDN