That's good.
Please make sure you create your set of W8 recovery media before proceeding to install W7 because after you install W7, the recovery partition will most likely no longer work.
See this guide for doing that.
Fortunately, your model is pretty easy to downgrade to W7 driver-wise.
Here is what you need to do for drivers for your model:
You can use all of the drivers from the HP Probook 4540s except the audio and card reader drivers.
Use the Intel HD graphics adapter driver for your model.
Audio: Accept the agreement, download and install the second driver on the list (64 bit).
The card reader driver from this model should work on yours.