I don't know how sacrilegious it is, but the more I look at my Smit Rotterdam Build, the more I visualize personal changes I like to make. I don't like the original colors, I think my boat would look better without the forward mast and to down-scale the main mast and also without the deck protection bars. I may even move the stacks just slightly away from the rear wheel house and place the stairs in between each stack and the wheelhouse.
That's just what I see now. I can't see going farther than that, but I'm excited to see the changes. the good thing is, these items can always be added on if I'm wrong.
So, should I be lined up and shot or can you see some fun?
It is your model so do with it what you want. The main question you have to ask, and it is more important than any about masts, decks and what 'should' be, is: Are you having fun?
If yes (accepting periods of blue air expletives and stuck fingers) then it does not matter what you do with your model.
I bet that on any website showing lots of photos of the class of Tug you are building, there will be differences in colour, equipment fit, Logo's, funnels, even fenders and what type of old tyres have been slung over the side for extra protection! And don't forget refits.
Have fun with the first model and then if you want, get more particular of the second vessel you want to model. I bought a kit of a WW1 Monitor M15 and have been turning it into M19 with a radically different turret and superstructure fittings.
You are doing fab, and are pacing yourself. But I would be very careful not to damage that lace table cover though, or you might not be allowed to play boat until it has been laundered snow white