A few months ago, I left a small software development company for another (based in the UK). I was leaving for better career development and exposure to new technology that the first company simply could not provide. Nevertheless, with my colleagues and managers, we parted ways on good terms. Nowadays, I know from my friends still in the company that they are struggling to find a replacement for me, the explanations for this are never given by the managers conducting the interviews - what few they arrange - and I felt it was inappropriate for me to ask further.
I recently received an email from my former CEO, whom I got along well with but only spoke to maybe once a week at most. She admitted what my former colleagues had mentioned, that they are having a hard time finding someone to fill my role. She reasons that as someone looking at the job's advert from the outside, I could offer suggestions on how to make it look more appealing. She at least confirmed that the job is indeed the exact same one I was doing before; no changes there.
As you might expect, my current employment contract says that I cannot conduct work for another company without first clearing it with my new manager. While I don't think this would count as 'work', I imagine it would still look bad on me if I am found helping my former boss. I have seen the advert and a possible reason for lack of interest stands out immediately; their offered salary is significantly lower than what I was getting (even compared to my first year in the job). I suspect - though cannot be certain - that the reason for the low salary being offered is because it is similar to what my co-workers earn, which may cause some disruption if I mention to my former colleagues or boss.
My questions is: Would it be appropriate to offer feedback on the advert of my old job?