Q: May the Dedication of a Church take place on the patronal feast day of that same community?
A: The third appendix of the Ceremonial of Bishops has a chart governing ritual masses and other masses. It states that ritual masses are not permitted on solemnities.
The Order of the Dedication of a Church says in paragraph 7 that the dedication cannot take place on a day when it is improper to disregard the mystery being celebrated. It then names the Triduum, Christmas, Epiphany, Ascension, Pentecost, Ash Wednesday, Holy Week and All Souls. Paragraph 8 says that the proper prayers from the ritual mass are to be used for the liturgy of the word and eucharist.
In short, the Ceremonial of Bishops is more restrictive than the order of dedication itself. To be on the safe side, I’d take the advice from the Ceremonial of Bishops.
There is a practical advantage to separating these events, as you know. The parish patronal feast is actually a solemnity for that parish, as is the anniversary of the day of dedication. It is kinder to the parish to choose a day that has no other conflict on the calendar for its dedication day so that the community may celebrate it appropriately in the years to come.