Hack and modify an existing APK

Here goes a quickie:
I have one of those cheap scales that tells you how much fat you have and it connects to a Android phone over Bluetooth. Such app has some glitches, errors and issues; yet it is operational.

I want to export the values to a CSV, TXT or XML file that I will mingle with and backup later; the PDF file functionality is already there and as crappy as it is I won't waste your time with it. Also, some of the values show up in the app but fail to be exported [lame developers] and I want those too [I also suspect there might be values and measurements that won't appear but are there].

Finally it has a limit of four users for the app, and this is a problem if you have a somewhat functional family [or a highly dysfunctional one]. I want to remove this limitation or maybe increase it to some absurd value like 999 for some Genghis Khan action.

I have some degree of knowledge on programming yet Android development is uncharted territory. I already managed to decompiled the apk in Linux but I don't have the knowledge nor the will to go exploring and ask around in forums... this is where we fit in. I could/can prepare a local setup with a phone, the scale and maybe a Raspberry Pi4 so you can do testing/experimenting yet I suspect a formal developer might get it working just by tweaking the APK. Extra kuddos if you help me to run it on Linux, maybe using Anbox or something more efficient.

I won't restrict this to full-time developers: I know there are a ton of broad spectrum hackers and tinkerers that can get this and more done.

I can get you some actual developer work if this goes right. Some with hardware, some more like software.

20240301 Still interested, no rush.