A pod after 1835 or so is preferred
I find it would be Interesting If Mexico Is allowed to succeed
Also would this allow for a more stable Mexico, or wold this not help it's real problems?
Now Was the Texas independence war Really close to failure on texas's part, or am I wrong
As some of the members have pointed out there is some ways of giving Mexico a better chance, but it is significantly harder. By 1835 Mexico has had a few coups and Santa Anna has revoked the 1824 Constitution and replaced it with one of his own design (which eventually lead to Texas and several other states to secede from the republic).
The earlier the POD the better. A few examples include the 1799 Conspiracy of the Machetes, if Mexico can gain independence during this time while the USA isn't as powerful then they get a head start at development. I have to read more on this but I think you can have a few butterflies make Bernardo de Galvez get independence for the colony in the 1780's or 90's. Also, having the start of the OTL Independence War in 1810 start off even smoother and subsequently become more powerful *coughshamelessplugcough* would do wonders for Mexico's future.
If the insurgents had decided to attack Mexico City in 1810 and succeeded taken it that could have shortened the war for almost 10 years and would give Mexico a better start, without having all the mining industry and agriculture abandoned.
Have the Mexican authorities be very firm in denying slave ownership in the Texas territory. Make it plain that paper trickery would not be tolerated, and that any “Negros” crossing into Mexican territory would automatically and permanently be free citizens.
That may only anger more the Texan colonists. Another focus should be applied, similar to OTL, giving the colonists some freedoms, but seeing enforced as well the imigration laws the Mexican government had implemented.