You are importing their public address, thus as you said it is watch only.
The only way you would be able to influence the coins on that address would be to import their private key.
In short, you cannot affect other users by importing a public address in watch only mode.
Hmm, I think seeing these kind of setup in your wallet will make someone greedy, making a plan or a trick to hack it, it is possible right?
No you can't hack it. Not can you hack the bitcoin network. What you can do however is use hacking and social engineering to gain access to someone's private key. If you gain access to someone's private key then you can access their wallet. So while you can't hack directly you can indirectly gain access to a person's wallet. Hope that helps. Was a good question btw
I'm going to stop you right there and call
BULLSHITEverything can be hacked. If you think otherwise then you're in for an inevitable rude awakening. And to be honest, more things have been hacked than you can comprehend(aka everything). There are no 100% guarantees. And you should live your life with that understanding.
The definition of hacking is not exclusive to writing code(that's called programming). You should purge such ignorance from your conceptual reality.
Social engineering for example,
is hacking and doesn't require the use of a computer.
Oh yeah, everyone that taught you that things are "impossible" has lied to you.
The traditional definition of hacking is to achieve something via skill, likely using an unconventional method.