Manage groups at Portfolio level as an option

Currently custom groups are managed across portfolios which is mostly fine. It will be helpful, if there is an option to override at portfolio level. For example, I've a category "non-performers" where I group all non-performing securities. For one or more portfolios, these securities are performing well, based on purchase date and price, etc. There, non-performing category is not applicable. If I've an option to override those securities grouping categories, it will improve the effectiveness of custom groups.