Would you consider using Tamoxifen instead of an AI in a post-menopausal women with ER+ and/or PR+ breast cancer who can't/won't discontinue hormone replacement therapy?  

I use tamoxifen in a switching strategy in many postmenopausal women anyway so the short answer is yes. The longer answer is that the ongoing use of HRT in this setting has issues that aren't solved by whether you use a SERM or an AI.