Question: Do you believe that Daniel ever struggled with religion or legalism because of his routine and/or discipline?
Answer:

I believe Daniel’s disciplined life grew out of His love and gratefulness to God for his mercy and grace. God’s love and faithfulness toward His people Israel is promised throughout Scripture. Daniel knew the Word of God and the God of the Word (Dan 9). Like all the great followers of the one true and living God whom we see in Scripture, Daniel truly believed God and His Word and lived accordingly.
Daniel came to undestand that throughout the Old Testament God proved His love and faithfulness to Israel over and over (Jer 31:3; Hos 2:14, 23). Daniel lived like one who knows and loves God!
Daniel studied and understood God’s Word (Dan 1:8). He trusted God — and the book of Daniel is a testimony to that fact!
So pursuing a life of loving obedience to God’s commands and promises is the natural response of one who has come into a saving relationship with the God of the Bible! We don’t see evidence in Scripture that Daniel practiced a “disciplined life” to be made right with God or to gain favor with God or others! On the contrary, this is the response of all who have come to personally know Him and His love and forgiveness! (Dan 9:7-8)
So Daniel knew he was sinful. And his life was marked by the attitudes and actions of one who had received the love and mercy of God.