There are many articles on the role that Lucille Ball had in saving Star Trek from an early death and how she advocated for the show in its early days. Was her role limited to funding, politics, and advocacy, or did she have any significant creative influence? For example, did she write any episodes, design any props, edit any dialogue, advise on fashion, or tell the director when Kirk should or should not fire phasers?
By all accounts, no other studio / network was willing to take on Roddenberry's new project called "Star Trek" - so her approval for producing the series at Desilu is probably the most important factor in even getting Star Trek made.
"If it were not for Lucy, there would be no Star Trek today" - Ed Holly, Desilu
Lucy was also tangentially involved in a very important hire, and a few others:
Lucille Ball's music director, William Hatch, recommended hiring Alexander Courage, composer of the iconic theme music
Lucille Ball knew and approved of Marc Daniels, an influential and frequent director of episodes.
The most direct influence (other than pilot / series approval):
Regarding Herb Kenwith, director of S3 episode "The Lights of Zetar":
Lucy "put a bug in Gene Roddenberry's ear to find her old friend some work on his show - the show her former studio had made possible. Roddenberry called Frieberger. Kenwith, who had never even seen an episode of Star Trek, was offered the job.
-- source: These Are the Voyages Season 1, Season 3 - Marc Cushman
I have never seen any account of creative influence. Just green lighting the series as the owner of Desilu which she sold after Star Trek's first season. Considering how well documented the history of trek is I think it is safe to assume the creative stuff was Gene Coon, Gene Roddenberry, Wah Ming Chang, and the writers...and that all the suits cared about was the budgets and censorship. Lucy is one step removed from even the network "suits". But she is absolutely important as the one who saw the potential appeal of it and had the power to get it started.
"Lucy had a good eye for spotting proposals with mass appeal"
"According to Solow in Marc Cushman’s history These Are the Voyages, Lucy initially thought Star Trek was about traveling USO performers. But her support for the show was necessary as it became clear how expensive the pilot would be. Lucy overruled her board of directors to make sure the episode was produced."