These are merely excuses to continue in sin and a lack of faith in trusting in YHWH to provide should they choose to obey Him. Do you not think YHWH will provide an even better job for them if they choose to obey Him by not working on the 7th day? Your "Sabbath on any day of the week" doctrine will not stand come judgment day. That does not mean such Christians will lose their salvation, but they most certainly will lose rewards in the Kingdom.
Preserving life and health is a valid reason for working on Sabbath. However, if such people can get the 7th off from such work, they should. Most nurses do not work seven days a week. Instead of getting off on Sunday, they can ask for Saturday off.
More excuses. Plumbing problems can wait until Sunday to get fixed.
I don't know what "doing it tough" means. If God commands something, then we are to obey. He has already commanded His people to not work on the 7th day. So if we hear a voice telling us to work on the 7th day, we better be very sure it is HIS voice and not our own or the adversaries.
There is no such thing as "the New Covenant Sabbath". The OC Sabbath has been carried over into the NC.
So if one is a valid reason. Why aren't the others? Everything I mentioned in that post and there is much more I haven't mentioned like Christian vetanarians helping out injured animals, Christian Cops doing their best to keep the communities safe, they are doing good on a Saturday.
So what's the difference? Especially when they start of the day in prayer and put the day in the Lord's hands.
The Christian working attitude, is in whatever you do, you do to the Lord, and not for your own sake, but the sake of others, for their good, for when you do good for others, you are also doing good for the Lord.
So let's look at Mark 3:4 again.
So is it lawful to do good to others on the Sabbath? Yes it is
Is it right to do evil on any day of the week? Of course not....
Is it lawful to save a life on the Sabbath? Yes it is.
Is it right to kill anyone at anytime? No way...