The iOS HIG discusses the best practices of a Tab Bar. Two points that are made that relate to your question are:
In general, use a tab bar to organize information at the app level. A tab bar is well suited for use in the main app view because it’s a good way to flatten your information hierarchy and provide access to several peer information categories or modes at one time.
Don’t remove a tab when its function is unavailable. If a tab represents a part of your app that is unavailable in the current context, it’s better to display a disabled tab than to remove the tab altogether. If you remove a tab in some cases but not in others, you make your app’s UI unstable and unpredictable. The best solution is to ensure that all tabs are enabled, but explain why a tab’s content is unavailable. For example, if the user doesn’t have any songs on an iOS device, the Songs tab in the Music app displays a screen that explains how to download songs.
In other words: do not change the contents of a Tab Bar based on a mode within the application. The Tab Bar act on the application as a whole, not the current view or mode.
It appears the same concept in the Android Design docs is the Top Level Switching With View Controls. Again, these are for app level navigation - not to be changed based on a view/mode.