To go to an interview for a job I can't take

This entirely depends on the organisation, if it's maybe a family run business or one where they value that kind of thing then yeah...

But I've just finished a recruitment drive for a large organisation, with no end of troubles, and to be honest this would just piss me off, you'd have wasted my time, your own, and everyone else's, and if anything I think it would just damage your name with the company. So much more goes into recruitment than on the surface, and this would be a massive NO for me!

You are likely to do more harm than good!
you can’t say at interview you aren’t really interested
if they offer it and you turn it down as it’s ‘below’ you you could put their nose out of joint for wasting there time

wait until they have a role at the level you want and reapply

You'd be way better off emailing to apologise you're declining the interview, because of the reasons you've stated, but that you love the company and hope to be considered for other roles in the future.

If I were a hiring manager it would make me remember you for future things, and I wouldn't be pissed off that you wasted my time scoring an interview. Everyone wins!

You are taking a spot away from someone who may need or actually want the job
You are very full of self imporrance i would not waste the company time and do the decent thing and give someone else a chance

Withdraw but tell them how interested you are if something else comes up?

Don't waste your or their time

Just go and see what happens. Recruitment can take ages, you might not get offered the job. If you do then see if there is wriggle room on the hours.

I always say that you can make a decision about whether you want a job or not when you get offered it
Of course if there is absolutely NO WAY you would take it then cancel but if there is even a small chance then go

No, that’s just wasting everyone’s time, effort and money.

Contact them to withdraw from the interview, but tell them what you’ve just told us! How much you’d like to work for them, and you hope they’ll bear you in mind if other roles come up.

Perfect.

Don't turn down a job you haven't been offered. Go, it could be really eye opening and potentially another role could arise that isn't advertised but more suited to you .

How do you answer the "what made you decide to apply for this job?" question?

Because you either lie and wax lyrical about how amazing the position is.
Or you tell the truth that you don't want it but are looking for something else.

I would find neither impressive, as an interviewer.

That's what I think

It sort of sounds like you think you’re utterly amazing and when you tell them you can’t take the job, you think they’ll create a new post for you.

I mean… it sometimes happens but do you know if they actually have capacity to hire you elsewhere in the organisation? Have you any contacts there? Because the most likely outcome is that they see you as a time waster.

We also go back to previous candidates sometimes. But not if we become aware that they have knowingly wasted our time!

If the OP goes for the interview, gets offered the job and then declines, it's very unlikely that they will be willing to consider her next time. Especially if it becomes obvious that she never had any intention of taking the job in the first place.

How would you answer the question "if we were to offer you the position, would you take it?".

I'm going to go contrary to what everyone else has said.

Where I work (large public sector arm's length body) we keep applicant's records on file for 6 months in a "talent pool" and do go back to unsuccessful candidates if an opportunity comes up in that time. If they interviewed at that grade, and passed the "bar" but were beaten by someone better, they may not even need to interview again.

Also, as part of a large recruitment campaign, we have interviewed candidates for Role A, but offered them Role B. Role B may not even have existed at the time of interview, but with big campaigns there is a lot of internal movement.

I’d go for the interview. You will be better informed afterwards whether it offers opportunity for promotion and growth. I’m sure they will ask why you are interested if it’s apparent that it would be a step down. Most people are seeking interviews for multiple roles simultaneously anyway. Are you currently working full time, and what would you do with your remaining hours if doing the dude hustle?

Nope, I wouldn’t consider you for anything else if you known knowingly wasted my time.

If someone wasted my time attending an interview for a job that that had no intention of accepting, I absolutely wouldn't be considering offering them an alternative role...I'd be noting that they're a time waster with no respect for other people.

It would be much better to contact them prior to the interview to explain that circumstances have changed, you're no longer able to consider the role because of xyz, but you're still really interested in working for them and will look out for alternative roles with them that might suit your circumstances and skill set. If they have something available, they might point you towards it.

I'd see you as a time waster and I'd be pretty pissed off with you.

Could you do the job if offered shorter hours to tie on with working around the side hustle? In which case go, and negotiate hours if offered the job.

Or scenario 3 - they hire you for the more junior role and you are constantly overlooked for promotion or other roles… because they have a highly qualified person happily doing the more junior role. You will probably also end up taking on more responsibilities that are beyond the scope of the junior role, to demonstrate that you are capable and striving. You will be an absolute bargain for the company. Why would they ever want things to change. They will have bought your expensive at very little cost.