I believe you can do this. 

When a warehouse is not configured for bin use, internally, it is still assigned to a special bin called "Default".  That is the bin that will contain all your quantities.  When switching to track quantity at bin, this bin will still contain all your quantities.  This "Default" bin does not show up in many of the navigators because it is not really used when bin tracking is used.  So after you flip the flag on the warehouse to track quantity at bin, be prepared to add any bins that you need, and then do a physical count, zeroing out any count cards for "Default" bins and entering count cards for bins that now house the items.  If the net inventory counts match exactly, there will be no G/L effect.  If there is shrinkage or extra units found, then there will be a G/L impact for the net increase or decrease.

If this is a warehouse that was just set up, it should be easy.  If it has been used for a while, it may take some time to switch over.  If you flip the flag without the physical count (or I guess even a bin transfer), you may not be able to select the inventory items for that warehouse as "Default" may not  be a selectable bin in the rest of the system.

I believe you can do this. 

When a warehouse is not configured for bin use, internally, it is still assigned to a special bin called "Default".  That is the bin that will contain all your quantities.  When switching to track quantity at bin, this bin will still contain all your quantities.  This "Default" bin does not show up in many of the navigators because it is not really used when bin tracking is used.  So after you flip the flag on the warehouse to track quantity at bin, be prepared to add any bins that you need, and then do a physical count, zeroing out any count cards for "Default" bins and entering count cards for bins that now house the items.  If the net inventory counts match exactly, there will be no G/L effect.  If there is shrinkage or extra units found, then there will be a G/L impact for the net increase or decrease.

If this is a warehouse that was just set up, it should be easy.  If it has been used for a while, it may take some time to switch over.  If you flip the flag without the physical count (or I guess even a bin transfer), you may not be able to select the inventory items for that warehouse as "Default" may not  be a selectable bin in the rest of the system.