I'm not a SN parent, but as a special ed teacher I'd say that you can redirect a child without telling them what not to do. The preschool classrooms I work with are set up on the assumption that in a well prepared environment, children will choose and carry out the activities they need to further their own development. However, sometimes kids on the spectrum need more support to do so, which is why I'm there.
I do redirect stimming if I think it's keeping a child from engaging in skill development (in the classroom -- I'm not one of those who thinks that every minute of a child's life needs to be about skill development) or if I think it's dangerous, or if I think it's innappropriate to the situation. If I'm going to do so, then the first question I'll ask myself is "what need is the stimming playing for that child at this time?" and then I'll let the answer guide the way I intervene.
So, for example if it's reading time and 7 year old A isn't reading because he's repeatedly lifting his body out of his chair with his arms like a gymnast, I might conclude that he needs proprioceptive input right now to organize himself, and invite him to go for a wheelbarrow walk in the hallway or get squished with a beanbag for a few minutes before he tries again.
If 3 year old C is humming and flapping her hands in front of her eyes at circle time because it's loud and overwhelming and she's trying to cut down on the stimuli I might see if she'd rather listen to circle while we work quietly with clay a few tables away.
If 5 year old J is sitting in the sandbox letting the sand dribble through his fingers over and over again, and has been doing that every outside time for a month, I might conclude that 1) he enjoys either the visual or tactile stimulation and 2) maybe his motor planning is preventing him from getting that stimulation in a more playful, less repetitive way. So I might invite him to help me "fix" the wheels on the scooters with a group of friends and some childsized tools -- so that he can stim a little on the spinning wheels, while still having a social experience, or I might put the hose in the sandbox and show him how to use his fingers to dig a path for the water (delightfully tactile) and then float leaf boats down his "river" (lovely visual stim).
For that matter, all children stim, not just kids on the spectrum, so I apply the same thinking to my own NT child. Let's say he's 4 and I take him to the theater, and he's running up and down the hallway while waiting for the show. Now, I don't object to running, but it's got his place and a crowded environment where I might lose him isn't that place. So I decide -- is he bored? If so I might swing him up on my shoulders and point out the colors in the flags decorating the hallway. Is he needing sensory input -- I might have him do some flips where I hold his hands, have him walk his feed up my body and land on the floor, or slip him a piece of chewing gum.
So, I have to disagree that redirecting stimming is always disrespectful. If your child's running up and down flapping and you say "stop that, don't do that, you're a bad boy" yes, that's not appropriate. But if he's running up and down flapping and you say "Hey Johnny, want to make some bubbles?" and fill up the sink with some water and detergent and hand him an egg beater so he can engage in some great sensory play, and he ends up with an even bigger smile on his face -- then I don't see that as harmful to his self esteem. Similarly, I would never tell my DS (who is 9, not 4, 4 is just an example) that he sounds bad when he sings, but if he's been singing in the backseat of the car for an hour and we're 4 hours from Grandma's I've been known to say "Hey, who wants to listen to Harry Potter on CD".