A BTO Call option Expires Next Day is $1.00 (Strike Price XXX). Next
day irrespective of stock price move, option Premium came down to
$0.30 as it expires same day.
So Can I buy the position, "Sell to Open" Call at $1.00, Next day to
"Buy to Close" at $0.30 for the profit of $0.70 ??
You wouldn't say you're buying that position, because you are actually selling a contract, but yeah you've got the idea.
When you sell an option contract you get paid a premium (receive a credit) and take on an obligation to buy/sell a certain number of shares (typically 100) at a specific price if the option is executed. Your maximum profit is achieved if the option expires worthless and you get to keep all the premium. As you mentioned you can also buy the contract back to close out your position, if the value has gone down then you can buy it back for less than the credit you received, netting a profit.
An important difference is the risk involved when you are selling options. When you buy to open a position your max loss is the premium you paid, but when you sell to open you can expose yourself to unlimited risk. Be aware that the buyer of your option doesn't have to wait until expiration to execute it. You have to be prepared to handle early assignment. I'd suggest researching things like covered vs naked puts/calls, margin call, and option spreads to start getting a good handle on the risk/reward propositions.
As for the question in your title:
“Sell To Open” a Call or “Buy to Open” a Put when Trend is Bearish
Both are bearish, which is appropriate will vary based on a lot of factors.