"T", as a middle initial, has certain powers and abilities which are not shared by other middle initials. "T" has the ability to replace other middle initials in an inexplicable manner. James R. Kirk was set upon by the middle initial "T" at some point in 2265 or 2266, and he became James T. Kirk. "T" traveled back in time to Kirk's birth aboard the USS Kelvin, and created an altered reality where James T. Kirk was never assigned assigned the middle initial "R".
"T" has an ability to take hold of a person's mind and make them say their middle initial every time they speak their own name. James T. Kirk lost all ability to refer to himself as "James Kirk". He spent the rest of his life, and indeed, the rest of history, with "T". Leland T. Lynch was also beset by this confliction—he had no choice but to say "Bridge, Leland T. Lynch here", every time he called. It was important to work with people affected by "T", as sometimes it might even seem tempting to respond as "Lynch, this is Data T. What-the-fuck-is-wrong-with-you".
Ro Laren successfully avoided "T", narrowly averting becoming "Ro T. Laren".
"T" has the ability to change the middle name referred to. William Thelonius Riker was transfixed with "T", but became "William Thomas Riker" later in his life. When he was duplicated in a plot device, Riker's duplicate promoted "T" to his first initial, becoming Thomas Riker. It is even possible that another "T" was created, a possible form of reproduction, thus making him "Thomas T. Riker".