could a priest enter the seminary of a diocese with the intention of only saying the tridentine mass and the 1962 sacraments? Does anyone know of a dioceean priest who only says the tridentine mass and not the novus ordo?
You could not do this. Like it or not, the OF is the predominant form of the Mass. A diocesan parish needs to be the sort of place where any local Catholic will be able to go. By not using the OF, a diocesan priest would exclude the majority of his potential congregation.
A second thing to consider is whether or not the parish will even want it. Understand, there are many people who will walk out and go to another parish if you try to bring about the EF. You could lose enormous numbers of people who will leave the Church or simply go to another parish because they will find your actions so distasteful. A diocesan priest who causes this will be considered a failure by many in the Church, and will most likely be moved to some tiny parish. Your intentions may be good, but it could end badly.
Ultimately, you would HAVE to celebrate the OF. A lot. You might not be the pastor. In that case, you would have to conform to what the pastor wants, and pretty much every pastor in the diocesan priesthood used the OF. If you are the pastor, you still can’t suddenly come to a parish used to the OF and say “Hey everyone, I’m gonna use a liturgy all of you are unfamiliar with, all the time. You cool with that?” As said before, people will get upset. You’d have to ease them into it very slowly. I know priests who have worked on “traditionalizing” their parishes, and it’s a slow process. In the meantime you’d have to celebrate the OF, and you would never be allowed to totally exclude the OF by your bishop. Even if you do get the EF part of the time, for all you know you’ll get moved to a new parish (trust me, sooner or later you will), in which case you’ll have to start all over again.
So no, you could not do this. It would be impossible to accomplish, and no diocesan seminary will want a man who will not celebrate the OF. The main purpose of the diocese is to minister to the laity, and most of the laity know the OF. They will not want someone who will not conform to that. Many diocesan seminaries don’t even teach the EF, and the ones that do still require you to know the OF. They will not make an exception in your case.