Removing lag screws corroded on strainer thruhull

[Goblinfog]

After removing my strainer thruhull to rebed, found that instead of using 4 bolts and nuts to secure the strainer through the hull, lag screws were used. Now I have 4 screws(heads are corroded off) going completely through my hull. The tips of the screws are just breaking through the inside of the hull. Any easy way to remove these. Also could I use epoxy to fill the holes afterwards, or would i have to reglass.

[Barquito]

Maybe drill out the lag screws, then replace with through bolts?