If you paste text with a trailing new-line into
cmd, then the text will be executed as a command immediately.
The easiest way I have found to avoid this is to select by clicking at the end of the text, then dragging to the beginning. If you accidentally include an extra new-line it will be before the text, which will execute a blank line, before filling the next line with the text you want, but not executing it.
Alternatively, you could use Kamil Maciorowski's suggestion, to type
::) at the start of the line before pasting, so that if the line does execute, it will be a comment, which can then be edited with history editing or cutting and pasting within
This effectively does what you ask, stopping a pasted command executing immediately, even if there is a trailing new-line, though I prefer to make sure that there is no new-line in the pasted text.