Q: since this predates the giving of Torah is it safe to assume that the day is still blessed and holy?
A: yes. The giving of the manna shows that the seventh day was holy before the Law:
he said to them, “This is what the Lord has commanded: ‘Tomorrow is a day of solemn rest, a holy Sabbath to the Lord; bake what you will bake and boil what you will boil, and all that is left over lay aside to be kept till the morning.’” (Exodus 16:23 ESV)
Blessing the seventh day was an act of creation which established the Sabbath. This act was no different than creating the sun or the moon or any physical object. The proof of any work of creation is its existence following the work of creation. The Sabbath is post-creation evidence that the seventh day was blessed and so remains blessed.
The Law given at Sinai, did not establish the Sabbath; it extended the Sabbath from an individual to a corporate obligation:
Remember the Sabbath day, to keep it holy. Six days you shall labor, and do all your work, but the seventh day is a Sabbath to the Lord your God. On it you shall not do any work, you, or your son, or your daughter, your male servant, or your female servant, or your livestock, or the sojourner who is within your gates. For in six days the Lord made heaven and earth, the sea, and all that is in them, and rested on the seventh day. Therefore the Lord blessed the Sabbath day and made it holy. Exodus 20:8-11 ESV)
In addition, Jesus is the Lord of the Sabbath (Matthew 12:8, Mark 2:28, Luke 6:5) and Jesus has authority over all things in heaven and on earth (Matthew 28:18). The dissolution of the Sabbath would alter His authority.
Q: What are the practical implication of God blessing and sanctifying the seventh day?
If this is seeking to understand the manner or nature of the actual blessing, then any answer will be speculative. However, there are some basic assumptions which can be made. First, the act of blessing would likely begin when the seventh day begin and continue until it was over. The events in the Garden of Eden indicate the LORD God was on the earth on the sixth day. Therefore He could bless and observe that day.
A meaning of bless is to kneel. [H1288-barak] It is possible the LORD God knelt for the 24-hour period. It also means to prasie, celebrate, or adore. It is possible the LORD God did this. While it is speculation, it seems likely actions constituting the blessing would be done on the earth by the LORD God and they begin when the seventh day started and continue until it ended.
The first man and woman would be present when the seventh day was blessed and so the knowledge of the Sabbath before the Law (as shown in Exodus 16) would come from the actual events.