Official modding support for Baldur's Gate 3 will arrive this September. That month is when the next major update for Baldur's Gate 3 will be released and with it will come the "officially sanctioned toolkit for giving Lae'zel a mullet."
The Baldur's Gate 3 Toolkit is available for testing right now. Assuming all goes well, it will be officially released as part of Patch 7 in September....