Hi,
Dropping and reload is depend on your requirement.
For added info object if you don't need historic data then drop and reload not necessary.
As you stated you can add to info object level as navigational attribute and mark as navigational at your cube level.do the identification at multi provider level.
Whatever way you do you need to do the changes on cube and multi provider are mandatory.
if you add info object at master data level, then you need to do the full load master data.
Other wise you can add info object at cube level by using remodeling , save and activate your cube.
Later you need to do the indentification at all multi provider where ever its been used.
But try do and test once at dev system and later move all changes to prod.
Thanks