can you install smart inline switch inside of light switch electrical box?

If you are extremely skilled and creative then that would be a solid maybe. They are fairly large out of the box, though you could remove the plastic housing and insulate them with electrical tape to reduce the size. You will then have to find a switch with a fairly small backside and then jam them in together, or get rid of the switch all together.

Additionally, you do need to reset them every now and again; usually every few months or when you change your wifi password. For that you have to disconnect and reconnect them, which might be annoying if you have to opent the box for every time.