Is it permissible to combine prayers (Dhuhr and Asr, an early combination) due to work circumstances that prevent performing them at their prescribed times? And is it valid to combine Dhuhr and Asr in the morning if one knows they will not be able to perform them at their original times?

It is not permissible to combine Dhuhr and Asr prayers in the morning, nor to delay Asr until the time of Maghrib, even with the excuses for combining prayers. The combination of prayers occurs between Dhuhr and Asr, and Maghrib and Isha, at the time of only one of them. This is only permissible during travel, rain, or illness, and work is not a permanent excuse for combining prayers. One must observe prayers at their prescribed times, as they are a priority. If work prevents one from praying, it is not permissible to continue in that work, for Allah Almighty provides a way out and grants sustenance to those who fear Him.