Ok the way i have come to understand weapon morphs after my third character is this:
To gain certain effects on your weapon you should have done what the morph says at least once (duh), but once is all it can take! I have had effects mentioning things I had only done only once, early on in the game and had already forgotten about, yet my weapon took on that appearance. I believe the morph system doesnt pull from your most frequently used spell or ability or anything, but instead, every time you meet the requirements for a morph it adds that to a pool, then when it comes time to upgrade your weapon in the road to rule, it randomly picks from that pool and bam! theres your weapon morph.
So far i have not recieved a morph based on something i didnt do. That at least works as far as i can tell.
Unfortunately the weapon system didn't live up to what it was hyped to be in most cases, your weapons morphs are not a fluid thing and they dont always suit your character like they should, but it is still possible to make some incredibly cool weapons if your willing to put in the effort.
Such as:
First hold off on your lvl 2 upgrades as long as possible! This will allow you to build a bigger pool of possible morphs and a better chance of getting something that other people arent patient enough to get. Lvl 2 is where you will get your first physical change to your weapon, the hilt.
Secondly, Save right before choose your melee/ranged chests! You are able to return to the sanctuary while on the road to rule, this will allow you to save your game while on it and check out your hero weapons after you have opened your chests, allowing you to look at all your weapons and deciding if you want to keep these changes. If you dont like them, use the xbox button to return to dashboard and load fable again, you will load up on the RTR with no chests open and your weapons back to how they were.
If you open the chests again you will get a different outcome! Rinse and repeat til you are satisfied!
I have been uploading many of my outcomes to the fable wiki so check it out for details on specific morphs, and PLEASE add your own findings, it only takes a minute thanks!
http://fable.wikia.com/wiki/Hero_Weapons
Ugh my fingers hurt... hope people read this.