How can I interact with a public non-open source program?

Hi, I want to repeat a transaction that is sent by hand on the example of one site (testnet) using @solana/web3.js.

I didn’t find a GitHub, there is only an example of transactions (first, second, third) and the site itself. Also, I have already read two topics with titles: «How do I interract with someelses’s public program on Solana?», «Get program parameters/types for existing program».

I have several questions:

  1. The most important question. Is it even possible (or just impossible)?
  2. If possible, how difficult and problematic is this and how can it be done?
  3. If I want to somehow change the parameters, in what ways can I decode the bytes?
  4. Is it possible to find the necessary data for interacting with this program in the source code of the site?

Thanks a lot in advance!

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