Call, write, or visit the office of your legislative representative. This page can help you figure out who that is. They have the ability to introduce a bill into the legislature that would change the law, and that's the best way to change a law like what you're trying to do here.
Be sure to tell the legislator exactly what you think should be changed (e.g. "We should change section ABC of the Texas Property Code, < citation>, to say that 'no landlord can charge a fee of more than X for Y in Z conditions,' or something similar.") Then concisely summarize your reasons why. Consider consulting politics for more strategy on who and how to ask to increase the probability of success.
Be sure to give some consideration to the reason why the landlords charge such fees and the costs they have to incur associated with lease assignments/changes. Try to craft a proposal that addresses those concerns, perhaps in some alternative way, and communicate the degree to which you think you understand and have addressed those opposing views. Also try to think about what new challenges or issues would arise if your proposal went into the law.
The job of your representative and/or their staff includes listening to (a concise presentation of) your concerns and how you think the law should be changed, and representing those views in the legislature. S/he also has other constituents, including landlords, to answer to as well, and has to balance those potentially opposing interests before deciding what (if anything) to do. The degree to which you think the representative listens and represents your interests may determine whose campaign you support (including who you vote for and what you say to your friends/neighbors/family) in the next election.
Another strategy is to negotiate with your next landlord to take those fees out of your lease agreement, and then the contract which governs your specific agreement might be changed to address this concern.
If you want to change the law for everybody, you might have to convince a lot of people that it's a good idea. If you want to change the "law" for what affects you personally, you might only have to convince one person (your own landlord) that such a change is a good idea, at least in your case.