Presuming that you won't be breaking the 100-Meter maximum lenght specification, a simple gender-swapping coupler should allow you to connect the two cables as you describe. There are a couple potential gotcha's however.
First, both cables would should use a compatible wiring scheme. Standard ethernet cable uses a Straight-Through layout, but there are also several other layouts, such as Cross-patch/Cross-over. If the cable in the wall is cross-over, be sure to use a straight-through cable to extend. Most combinations will work, but there are a few to be careful of, especially if the nics in one of the connecting devices don't support auto-pin mapping (MDI-X)
Second, you may notice that after installing the coupler, that power/signal drops, and you are resending more signals than is optimal. in that case, some kind of active repeater/bridge/switch will be required. if you have seen powered devices online, these are essentially single port repeaters, which boost signal as it passes through. Note however that a repeater is an analog technology, and will amplify noise as well as it amplifies desirable signal. if there is too much noise on the line, only a fully fledged digital device like a switch or bridge will fix that.