This hex edit alone will make Mario get a fire flower instead of becoming big under the same conditions as the original game (that is, only if he's small):
This will remove that conditional (so Mario will always get a fire flower, regardless of his current state):
If you don't want Mario to get a fire flower if he already has a cape, apply this small patch instead of the second hex edit:
autoclean JML CapeCheck
+ JML $00F2E8
None of this is tested and it's 4 AM, so make a backup first!
e: lol I swear I spent 10 minutes checking that branch, but this is sleepiness for you. Thanks James!