Is it possible to use molly bolts in concrete?
A machine screw anchor is a good option for repeated removals and reinstallations. They're also available in standard thread sizes, so they can accept machine screws, eye bolts, or hook bolts. The downside is that you'll have to buy an inexpensive but specialized setting tool for each size of bolt you want to install.



The installation process is much like that of the lag shield below, except that you'll have to use the setting tool (third step) to seat the machine screw anchor into the hole.



Image Source

A lag shield anchor may be another acceptable option, but it is not as "reusable" as a machine screw anchor. It creates a sleeve inside the hole in your concrete with threads for a lag screw to grab onto. When the lag screw is inserted, it expands the shield inside the hole.

The installation process:


Drill appropriately sized hole with a hammer drill and masonry bit
Remove concrete dust
Tap lag shield anchor into hole
Insert lag screw into lag shield and tighten




The lag screw will still be removable, but keep in mind that many repeated removals and installs may eventually weaken the anchor.

Image Source 

(I have no affiliation with either distributor, they just had good illustrations.)