Are they interchangeable?

Yep they are.

裡 = 衣 + 里 = 裏. They are the same character but just different ways of combining 衣 and 里. The current trend is to combine the characters horizontally like裡 instead of vertically as in裏. So 裡 is now the standard form in Taiwan. Another example is 峰／峯. The horizontally combined 峰 become the standard form.

But actually, 裏 is the original form and 裡 is a relatively new comer. As this link shows, http://dict.variants.moe.edu.tw/yitia/sa/sa03732.htm most ancient dictionaries only list 裏 while 裡 is rarely seen. I think most Chinese still hand write 裏 instead of 裡 except those living in Taiwan.