Never heard of Liang Model Zimmerit Paste until now. Cannot recall anyone around here using it. Looked it up and watched a guy on YouTube applying the stuff. My impression is that it is very expensive spackle. Based on the video I watched, I would be very concerned about crumbling and/or peeling. The fast dry time will make it very hard to sculpt the stuff and correct mistakes.
The usual method to prevent putty from sticking to tools is to use an appropriate solvent. The idea it to create a very thin layer of solvent on the tool. When putty starts to stick to the tool, clean it off and refresh the solvent barrier layer.
Not that long ago, Wade (Armor_Buff) wrote a journal in which he tried various products to apply zimmerit: Make your own Zimmerit with Tamiya Gray Putty & Testor’s Liquid Cement. Even if you use a different product, his explanation of the application method may be useful.
There are lots of YouTube videos on making zimmerit using all sorts of products and tools. I suggesting watching a few videos until you find a system and result you like.
Here is a Jagdpanther I recent built. The zimmerit is Standard Milliput applied with a popsicle stick using water as a solvent. I am not saying you should use standard Milliput. I am suggesting that some versions of zimmerit are pretty easy to do and do not require any special tools.
In my opinion, you are doing exactly the right thing–experiment. You need not even sacrifice a model. It is super easy to practice making zimmerit rows and squares on a piece of box cardboard.
Here is good website describing zimmerit patterns: Zimmerit.