As for the snails, you can put super glue over the opening of the tubes. For spot feeding fish I use a SeaSquirt which is a long turkey baster available online and in some local fish stores.
They are harmless filter feeders. Getting all their food from the water column. Keeping your water extra clean for a while will help keep their numbers in check.
Target feeding usually refers to a method of feeding corals where you spray food right at them rather than letting them collect food from the water column.
I don't know how large your tank is or if you have any Wrasses or not but manually keep the Vermetid Snails in check by cutting into them with my bone cutters and my Wrasses do 'clean up'. They know exactly 'What's Up' and follow my cutters around in anticipation for a good meal.
You can crush the base of the snail with hemostats. You can also manually feed your fish from hemostats but it may take time for them to get used to it. The vermetid snails will eat poop and detritus out of the water column too though. So spot feeding won't completely solve your issue.