Moving toilet to opposite wall

This really depends on the stack itself. If it's cast iron, you would need to replace it all. If it is plastic, you can cut the branch out and insert a new branch facing the desired way. This is not ideal though - you may as well replace the whole stack.

Hi you can re use the old section and fittings as long as they are in good order as long as they will reach the new wc position

Yes it's possible to move the loo to another position. All you may have to do is arrange the COLD feed to where the new toilet positions to be sited and "CORE"drilling a 12cm or125mm hole through the wall ( average height from floor to spigot centre 18cm or 180mm) from finished floor level (FFL) The "PLASTIC" virtical stack should be okay clipped secure, allowing for a swept 4" Tee (whether solvent weld or push fit type) ...my advise is to keep to the same current plastic consumables soil stack material as the existing virtical left in place. Add your connections accordingly and NOT to cut too low. Remember you'll only need a slight fall to the stack from the loo NOT a 45 degreer This MAY or will result in a lost TRAP syphonage and bring funny smells to the home if the trap is lost... Phew..🤮 Hope this was helpful Good luck👍 pd