6. Edition Bleibt im Spiel Zauber

ja, das geht, dazu gbt es auch schon diverse FAQs...

Q. Can a single enemy unit be affected by multiple 'Remains in Play'
or lasting effect spells which do not specifically state that
this is allowable / outline the affects?

A. There's no problem with casting multiple spells on the same unit,
and normally the effects will be cumulative – i.e 2 Flames of The
Phoenix would each have chances of causing damage. On one-off effects,
such as Rain Lord, then the effect is a blanket rule which won't be
improved with multiple castings – in this case, you can't make them
any wetter with two spells than you can with one.
S. Gav Thorpe - Warhammer Design Team


Q. Can a unit be affected by the Slaanesh spell Luxurious Torment
several times, thus suffering additional damage at the start of
each turn?

A. Yes.
S. Anthony Reynolds - Warhammer Design Team (Online Q&A on the
Games Workshop Warhammer Forum)