Is the modify button not there at all, or are you just unable to use it?

The modify button was invisible

Did you do what it last told you to do? Dialogue won't appear in the tutorials unless you follow their orders. That will allow you to go and access the modify station button.

Yep, I followed the dialogs ;) The point is that I've been able to upgrade all the other railway stations and to add one platform and/or to lengthen them. All except Cherry Station.

I eventually got rid of this annoyance by destroying Cherry Station and building one again. But I noticed I had to re-build it one square right from its former position, in order to allow it to receive one more platform. I guess the terrain left to the station is the thing blocking its expansion.Not sure I understand why, though. Is this terrain unavailable for sale ? But if it was the case, I guess many other players would have hit the same problem and we would have tons of anxious thread about the topic. So, the mystery remains unsolved (for me...)

Okay, another issue on this tutorial now.
I'm a the point where I'm supposed to build loops or switchbacks at the two ends of my lines.

The northern end station has been built some IG months ago. I relaize now that I can't expand it because the Construction Material Storage blocks the line - and is not available for sale. So, I guess the only option left of to destroy the station and build a new one a few squares south.
Well, it's the tutorial and we have huge amounts of cash so the company can aford the price, but why didn't we have some warning when the building ofthe station took place. Or at least some prepared location to set the station in? It's a tutorial, right ?

Anyway, okay, at this point I had to destroy/rebuild 2 of my 4 stations. Let's say its the learning curve.

Now, what about building this loop on the southern station ?
Guess what ?
A Boutique has been built two squares behind and forbids to build any track.
And for some reason, that Boutique is also unavailable sor sale.

So what ? Shall I have to destroy/rebuild a third station, now ?
Is the tutorial broken or am I missing some important point ?

When I played the first scenario I was never blocked by any construction material storage, so I'm wondering how could you be blocked by that because they are not located in a way that they prevent to build a loop line around the island.

At some point in the tutorial they introduce the menu for building and destroying storage spaces, if a storage space is in the way, you have to destroy it using that menu, not with the menu for buying or selling land.

If you want to prevent a building to be build on a free space where you plan to lay a track, then buy that land.

This is a common error on the first tutorial. Did you speed up the game too much?

Ha, yep, maybe that thing. I usually set the speed to max to reach the next step when I'm finished with the todo list of the moment, it's too boring otherwise.

So, what you are saying is that at this point of the tutorial I am supposed to have those additional menus which would unblock me, and because I'm late on schedule I don't have them yet ?

Makes sense - although in this case, a warning in the tuto could be much welcome to avoid this kind of issues ( < this is a note to the @dev )

What would you advise me ? Do I leave this loop thing aside waiting for the buttons to appear, or do I destroy/rebuild the station despite the cost ?

You would have to destroy the station, build a new one, and then reconnect the line to allow for the depot button to appear.