renaming elements without activating aliases? Yes we can!
The dimension editor and dimension worksheets cannot rename elements directly, so let me introduce you to SwapAliasWithPrincipalName.

This a short simple syntax to easily pad zeroes to an index value:

Period = 'Period ' | NumberToStringEx(index, '00','','');

(from olap forums)

Comments allow you to explain, to yourself and/or to your users, what the query is trying to achieve, how it works, who wrote it or amended, etc.

Use "//" or "—" (without the double quotes) to end a line with a comment or to have the comment on its own line.

A query can be broken over multiple lines to make it more readable. For example:
{
FILTER(
     {TM1FILTERBYLEVEL( {TM1SUBSETALL( [Product] )}, 0)},
       Test2.([Rate Measures].[Rate]) = 19