In principle, you could add 50% energy to the motion that goes over the reaction barrier, which moves you up some of the vibrational energy levels .. and then another 50%. But in reality, that's going to be hard because in most molecules, there are dissipation mechanisms -- so it would be very hard to "keep" the energy in the motion (vibration) needed to overcome the reaction barrier.
Sometimes it's useful to use metaphors when talking about kinetics.
Let's consider that you need to jump over a barrier to get from a starting point to another place:
If the figure attempts to jump 50% of the height, it's not that they can jump another 50% to get over the wall.
In detailed chemical kinetics theory, molecules will have a distribution of different energies (the Boltzmann distribution) but either they have the energy to go "up and over" or they do not and stay on one side of the reaction barrier.
Now this metaphor isn't perfect because some chemical processes (e.g., heating water) can use repeated additions of energy. Also, few chemical reactions are one dimensional and some reactions occur via catalysts or quantum tunneling, so they're not really "jumping over" a barrier.
You might wonder, what happens to the first 50 kJ/mol. In the metaphor, the figure "falls back" because it does not get over the wall. There are a few mechanisms in which the molecule may dissipate energy, for example going into translational or rotational kinetics, or other low-energy vibrational modes.