To make items reservable (and specailly to be able to fullfill reservation when doing checking, which is standard procedure
when items get from closed storage to pickup desk) we modified all notforloan values which we use (like "only for work in library") to use negative values:

mysql> update items set notforloan=-2 where notforloan=1 ;
Query OK, 99196 rows affected (8.04 sec)
Rows matched: 99196  Changed: 99196  Warnings: 0

mysql> update items set notforloan=-3 where notforloan=2 ;
Query OK, 151 rows affected (1.50 sec)
Rows matched: 151  Changed: 151  Warnings: 0

mysql> update items set notforloan=-4 where notforloan=3 ;
Query OK, 247 rows affected (1.61 sec)
Rows matched: 247  Changed: 247  Warnings: 0

This works because of koha feature that items from acquisitions have negative notforloan.