Mass products update: Categories
Also, you can find this extension in Mass Products Update PACKAGE

You can update Products Links to Categories for multiple products at once, from admin page.
It works with an infinite number of products.

You can filter products by the following conditions:
– Product Name
– Product Tags
– Model
– Categories (multiple selection is possible)
– Manufacturers (multiple selection is possible)
– Filters (multiple selection is possible) (v1.5.5+)
– Price (base price): greater than or equal to a value, less than or equal to a value
– Discount Price: greater than or equal to a value, less than or equal to a value, customer group
– Special Price: greater than or equal to a value, less than or equal to a value, customer group
– Tax Class
– Quantity (stock): greater than or equal to a value, less than or equal to a value
– Minimum Quantity (Force a minimum ordered amount): greater than or equal to a value, less than or equal to a value
– Subtract Stock
– Out Of Stock Status
– Requires Shipping
– Date Available: greater than or equal to a date, less than or equal to a date
– Status
– Store
– Attribute
– Attribute Value
– Option
– Option Value

Products for update:
Filtered products will be listed with pagination, so, it works with an infinite number of products. 
You can set how many products shown per page (for slower servers or large databases, it is recommended a smaller number of products per page).
You can deselect or reselect certain products from list.

Products Categories Updating can be done in the following ways:
– Keep all old assigned categories and add selected categories. (A new category may be the same as the old one)
– Unset (unassign) all old categories and add selected categories. 
– Unset (unassign) selected categories from selected products.