Hi, hello again.
Are you sure running a full restricted CY over there in England? Where did you get your bike from?
But to answer your question, opening up a restricted CY50 Muffler is a hard and rocky way. You would need a lot of skill in grinding and welding too. Also a good and untouched CY muffler is very scarce and worthy, i wouldn't risk to destroy it.
This is a pic of a XL50 muffler, th CY ones are quite equal.
There is an inner 12mm pipe going all through the header. It starts right at the joint to cylinder head and ends in the middle chamber of the 3 chamber muffler (red).
Next pipe leads the gases back into the first chamber (yellow).
A third pipe brings the gases into the third and last chamber (green), from where they escape into freedom (blue).
View attachment 274192
To get an aftermarket pipe on webike (from Japan) for an Ape50/100 is easy, but needs a lot of work in customizing too.
So i would try to get a CY80 muffler in good shape, even harder to get than a 50s, but maybe.
Alex