Suppose I want to write $n!/2$, can I just write $\tfrac{1}{2}n!$ or is that easily confused with $(\tfrac{1}{2}n)!$ and I have to write $\tfrac{1}{2}(n!)$?
Are there precedence rules for these situations (like we have in Computer Programming languages C/C++/Python ...)?
It is a Common Convention that $n!$ is always taken together.
Compare $\sum n!$ , it is $\sum (n!)$ , not $(\sum n)!$
Compare $\log n!$ , it is $\log (n!)$ , not $(\log n)!$
Likewise $mn!$ is $m(n!)$ , not $(mn)!$
Thus $\frac12n!$ is $\frac12(n!)$ , not $(\frac12n)!$
When we want the other way , we have to use the Brackets.
When Context is weird , always use Brackets to aid the readers.
ADDENDUM :
Checked with Wolfram , which agrees with this Convention :
We can see that Wolfram is not taking $3n!$ to mean $(3n)!$ , where $n=2$ will not work.
Wolfram took $3n!$ to mean $3(n!)$ , where $n=2$ will work.