So, the thing to understand is that, unlike Shimano and some other brands, SRAM cranks are not different between Boost and non-Boost. However, the chainrings are offset differently, so a Boost chainring will sit 6mm further out from the BB.
What this means is that you can change a Boost to non-Boost (or vice versa) 1x setup by simply changing to a chainring that’s appropriate for your frame.
Whether you actually need to or not will depend on your frame / desired chainring size. My personal opinion is that if you can get away with running a non-Boost chainring on your Boost frame (i.e. no clearance issues) then that’s the way to go. This gives you a better chainline in the larger sprockets.
I don’t actually know how this all relates to 2x setups and spiders, but certainly you can just use a new 1x Boost chainring on your existing cranks.
EDIT: I missed the bit where you were saying you were using an older 2×10 speed XX crank. That doesn’t have a detachable spider. So it may or not work – it’ll depend if the tabs on the crank and the chainring itself clear the frame. I’d bet they would but you may have to just try it.