I think you’d have to make a global, say, current_zero, which you set from the raw value when pressing the TARE button. Then take the weight from a template sensor which computes the weight - current_zero
I’m not answering the question but answering a question you didn’t ask. So ignore as you see fit…
I had high hopes for a scale I could use to keep track of my propane cylinders current volume (translated from weight) but after a couple of years of trying I gave up on them entirely. The issue was that the load cells/circuit was way too temperature dependent. the weight would vary several pounds (out of 37 total pounds for a full tank) over the course of the day as the temp went up and down. It was way worse in the winter as well.
I never tested them in a temperature controlled environment so I can’t say how stable they will be. But I charted the weight vs ambient temperature on two different scales and it was pretty much a 100% correlation. Unfortunately I wasn’t smart enough to get a reasonable temperature compensation equation worked out. Mostly because of the differences between variations of weight over 10F to 40F in winter and 60F to 90F in summer. It wasn’t linear.
all that to say beware if you are using them outside.