Is it possible change the runway (and STAR) during approaching, because of wind or step aside?
PF3 scans for AI aircraft activity and will use the same runway being used by AI. If no AI are active, PF3 makes a runway assignment based on wind. You can request a runway change after the runway assignment has been given. Regarding STARs, PF3 does not use Navigraph data, so if you are flying an approach at pilot's discretion, you are not vectored and can fly at your discretion to the assigned runway (or enter the procedure in your FMC).
Is it possible to use 2X, 4X rate, during the flight?
This is not recommended or officially supported but individual results vary. I use 2X (at cruise only) and very rarely have problems.