Instead of doing that, have you looked into Tile Master or (when Cobra's apps come back) Super Tile? You can combine attributes from multiple devices into one tile, saving you some space on Dashboard and effectively achieving what you want--which I'm actually not sure how you plan to with a single device right now anyway, given that the stock dashboard templates would still limit you to displaying only one attribute (either contact or lock) from the device.
Alternatively, you could consider something like this: if your Dashboard is currently, for example, 6 tiles wide by 5 tiles tall, consider making it 6x10 instead of 6x5. Then, specify all of your "normal" tiles to take up 2 rows instead of the default of 1. This should make it look more or less like it did before (you may need to adjust font settings to your liking). Then, for your lock and contact sensor tiles, create two as normal but make them 1 row tall in the same column. They'll look half-height in comparison--a neat trick you can use to achieve something like you want without the need for custom code.
