A thought occurred to me: for those who read Tehillim according to a monthly schedule, are there any rules/regulations regarding or prohibitions against or problems with reading the same chapter twice in a day, aside from those that are meant to be said more than once, such as Ashrei (ch145 + extra verses)? So, for instance, if it is a Wednesday and it is the 19th of the month, does one say ch.94 as part of Shacharit or when reading the chapters for the 19th of the month (ch.90-96) or both during Shacaharit and during the time one sets aside for Tehillim reading?
The Psalm of the day is said as part of davening and is unconnected to any recitation of Tehillim that you may decide to do otherwise.
There are other Tehillim besides Ashrei that are repeated, BTW. The Sunday Psalm of the day (number 24) may be recited up to 3 times in the same day if that Sunday is a fast day. Granted, that's part of davening.
AFAIK, any Tehillim may be said as often as you wish.