1. Soccer was a regular subject in many public schools in England in the early 1800s. These schools developed their own rules, which were different from school to school.
2. Soccer was a regular subject in many public schools in England in the early 1800s. These schools developed their own rules, and they were different from school to school
3. Soccer was a regular subject in many public schools in England in the early 1800s. These schools developed their own rules, but they were different from school to school.
(Which one is similar to #1, #2 or #3? Can ",which" be changed into ",and they" or ",but they"? Which one is right?)
The first and second sentences are correct. They mean about the same.
In sentence 3, "but" is not the right word.