When I read the OP there are two disting things that I see: Either switching or topping as service. So I'm gonna answer the question for both options...
Switching as in really swapping roles with me being the dominant will NEVER happen. EVER. That is really a set-in-stone hard limit for me. In a D/s relationship one of the utmost important factor for me is that the roles and dynamic are clearly defined. I need that to feel safe and comfortable. Switching would take a lot away from me and the dynamic and to be honest I would most likely want to end a relationship if switching was needed for the other partner with me.
Topping as service is different than switching though... It's like how Leo described here:
I was still trying to bend things my way; simply doing it from beneath. I'm almost always a top but can be in the mood occasionally to be a bottom - but even then my mind is still a dom
There are dominants who do enjoy being on the receiving end of sensation play, some even are masochists. When topping as service happens the Dom tells the sub what to do. They are still in control while being bottom.
For ex. A Dom would tell his sub to spank him. He will tell how many hits, where to hit, when to stop, etc. Just because the sub gives the spnking does not mean he/she is dominating the Dom as they are still following orders.
I did that a couple of times but am highly unlikely to ever do so again. I didn't enjoy that for the same reasons I mentioned for switching. Even topping as a service would create mixed feelings and messages and put me in a bad headspace. I can't say I could not but I prefer playing with someone who is on the same page as me about this.
So to both options: Nope. Not gonna happen