New job, but not changing visa status?

I'm currently an ALT in Nagano, but I've applied for eikaiwa jobs in Osaka.
I have an Instructor visa that expires in 2019.
From what I've read, eikaiwa jobs require a Specialist in Humanities visa.

The one eikaiwa I really like said that I wouldn't need to change my visa status until 2019.
When I renew my visa in 2019, I can then ask for it to be changed to Specialist in Humanities.
I've read that it's technically illegal though.
If I do this, will there be consequences?
Will my visa not be renewed?

I'm confused as to why the eikaiwa would recommend that.
The eikaiwa has a great reputation and great employee reviews.

*** I did post another question about changing visas.
That was about the process and timeline.
This question is different.

if you want to know which option is best why you do not contact immigration directly?
They can inform you the right way and how to proceed.

Sorry for saying but I do not understand why you not ask them, maybe you want advice from forums but you will get many different answers.

Because going to immigration is very far for me.

This is one of those things where the rules say one thing, people do another. Technically yes, you are supposed to report and change your visa type for the different type of work. But a lot of people don't and swapping between eikaiwa and ALT without changing until is so common that it is unlikely to result in more than maybe a scolding from the immigration officer. I went through the same situation a few years ago and did the paperwork properly when I changed, and my company actually asked why I was going through the paperwork hassle when it had never been a problem for anyone. So it's a risk in the sense that it is illegal, but it's unlikely to have serious consequences.

To justmyday,
Nothing is wrong about the OP coming here to ask about it, in the sense of asking if anyone else had a similar situation as his.

To Lost,

Obvious: if they can hire you with the current resident status you have, which is a resident status that allows you to teach (though at different kind of institutions), you can start working for them right away, without waiting for the new one getting approved. They might be thinking it would be OK because the requirements for Humanities/International Services/ Engineer and Instructor resident status when it comes to teaching English are similar, also the documents they review are the same/similar, namely, either a bachelor's degree or three or more years of teaching experience, employment contract offered at a reasonable salary.

When it comes to the legality of this, or the possible consequences, I don't know.

@AK

so you react to others but you do not know the answer or even if you knew the answer than we can verify that it will be correct. This is why I said contact immigration, they know better and also immigration can inform the right procedure.

If you inform the OP in correct how will this solve the question. It can make it only worse.

But again thank you for replying and not give the answer OP is asking.

justmyday,
At least I answered the part about where he was wondering why eikaiwa would recommend that, though I admit I was not very helpful. I guess OP was looking for something like what Vita provided, not the official view by immigration.