Plenty of actors are interested in shaping their characters themselves. They want to give input to the writers and producers to make the role their own, but Star Trek: Voyager's Robert Beltran kept his requests to a minimum largely due to the number of characters on the show and the number of episodes that ran each season.
In an interview in the August/September 1997 edition of Star Trek Communicator, the Magazine of the Official Star Trek Fan Club, Beltran acknowledged that "we have basically 26 episodes to do a year, divided by nine characters." He went on to say that he was "content to be a good support for somebody else's episode."
Though there were a few times he asked for a little more, for the most part, he didn't try to get at the forefront of more episodes. He did mention he made some minor requests and there was one large one that got denied. In the second season episode, "Manuevers," Beltran's character, Chakotay, was captured by the Kazon when he infiltrated their ship. Beltran wanted to have the torture scene with "12 or 15 stuntment kicking the hell out of me, but we couldn't do that!"
Beltran went on to say that suggestions were welcome, but the actors didn't always get what they wanted. He did insist on running down a hill in one scene, but the producers wanted to use his stunt man. Beltran threatened to quit if he couldn't run down the hill himself. That led to conversations among the higher-ups, and Beltran was allowed to run down the hill, but with the requirement that there be somebody at the bottom to catch him.
Beltran did have some standout episodes where Chakotay took center stage, with one in particular being the season four episode, "Nemesis." Chakotay's shuttle was shot down over a planet, and he was led to believe that the Kradin were the enemies of the Vori and wanted to eliminate them. Over the course of the episode, Chakotay begins to hate the Kradin as much as the Vori do. But then he learns that he had been part of a brainwashing program, and the Kradin weren't the enemy. This leads to one of Chakotay's best lines in the series: "I wish it were as easy to stop hating as it was to start."