Mastering & remastering is when a professional mastering engineer takes the song and adds a final level of polish & shine to it with high end gear & their unique skills, ear & experience. They help bring out the best in the songs while helping them all feel coherent & related.https://twitter.com/baltmatrix/status/940226545859342341 …
No, they don't change any effects. They do EQ & compression to the overall sound, as well as adding saturation & other subtle tweaks if needed