Can I take a practice throw during the round?

No. A throw that is clearly not related to the competition is a practice throw and costs 1 penalty throw. The practice throw itself isn't counted (rule 809.03).

From 2027 these are not throws at all, so they carry no penalty (rule 802.01):

• Setting aside an unused disc, or tossing a disc back to a player, where it travels less than 5 meters in the air.
• Dropping a disc (unless you are deliberately dropping or placing it into the target to finish the hole, which counts).