It could be done easy by replacing the relevant Govt agencies involved heads and staff. Start enforcing existing law. Nothing new is needed to do that.
What "existing law" authorizes the President to simply grab billions of dollars from money people are sending to Mexico?
Executive orders and regulations aren't magically powerful, though they sometimes seem that way. That's why Obama was shot down on his immigration bill, and on his air regs. His actions lacked proper statutory basis. There's nothing even remotely close for this.