Mostly yes.
For starters, since you’re praying the office privately (as opposed to an official parish celebration), you may celebrate those days if you choose.
Here’s what the General Instruction says:
243. In individual celebration, the calendar of the place, or ones own calendar may be followed except on proper solemnities and feasts.
As long as the day isn’t a proper solemnity or feast, yes, you can celebrate that saint if you choose. To put this into perspective, what the Church is saying here is that this is different from a parish celebration, or one in a monastic community, where one person is imposing his own personal preference on the rest of the community. If you’re alone and you want to celebrate a certain saint, then you’re unanimous in that.
For clarity here, the words “ones own calendar” does not mean a private calendar. It refers more to the calendar of ones home diocese if he is travelling, or the calendar for the religious order if a priest is stationed in a diocesan parish, or similar examples. However, the principle still applies.
Keep in mind that you’re still praying the office, and this is the most important value here. The office itself won’t change, only your choice of text will change.
As long as it’s not a proper solemnity or feast, then by all means feel free to pray the appropriate hours for any saints you choose, in private.