Depending on the size hook I'm using, I either use the whole clam or cut it in half down the center. I leave everything attached to the clam and tie it on with clam string. See my video "how to bait circle hooks" for a demo.
If you mean can you thaw out frozen clams and salt them, I've never tried. After I salt fresh clams, I keep them in the freezer, but since they are salted, then never freeze solid and they keep a very long time.
I've never heard of using those for bait but I imagine they would work. I know someone who uses soft shell crabs for bait. Give it a try and let me know how you do.
Salted clams will last all season. A friend of mine keeps them in his truck but I suggest to keep them in a cooler while using them and put them in a refrigerator between fishing sessions.