The phrase 'but not preferred' is correct and usable in written English.
You can use this phrase when you want to express that something is an option, but not an idea that is favored or preferred. For example, "You can have the drink with no ice, but not preferred."
The weak autumn sun had long set by the time a senior palace aide, perhaps even the Queen's private secretary, Sir Christopher Geidt KCVO OBE PC, welcomed his fellow counsellors – "councillors", of course, is acceptable, but not preferred – into the silk and gilt-trimmed splendour of the 1844 Room for the ninth meeting this year of Her Majesty's Most Honourable Privy Council [see footnote].
Furthermore, physical intensities (material, energy and emissions) are suitable, but not preferred for holistic industry decompositions, because of the large varieties in physical units involved.
Valid identifiers point to valid but not preferred stereoisomers, invalid identifiers point to invalid stereoisomers or mixtures, incorrect identifiers point to different compounds, and nonexistent identifiers do not point to anything.
Cards -- a common holiday practice -- were allowed but not preferred by the prisoners.
Don't leave pennies or excessive change on the table; if that is all you have on you it is considered better than nothing but not preferred.
They do, however, vary in their preferences for innovations aimed at specific population groups: preferring investment in innovations for people with 'disability'cancerncer' and 'asthma' , but not preferring investment in innovations targeting people with 'drug addiction' and 'obesity'obesity
If you are 12 or under but you are very tall, you can wear tall boots but it is not preferred.
I used it without an object; common usage has made that intransitive form correct, but it is not preferred in formal writing.
Computerised assessment was valued by the professionals, but it was not preferred above the conventional paper assessment by the patients.
Composite outcomes are generally also not preferred but accepted if clinical trials reporting single outcomes are not available.
