It can be argued that the clear commandments of God in scripture could be used to require that a person repent of specific sins before being allowed to be baptized, but in the case of the Word of Wisdom, the Lord expressly stated it was to be “without commandment or restraint” (D&C 89:1-3), making it a subject off limits for baptismal requirements.
Regarding tithing, it is a “standing law unto the church” (D&C 119:4). It is commonly thought that baptism makes one a member of the LDS Church. While valid and sincere baptism defines a member of Christ’s church, and establishes a relationship between the convert and the Lord, the association of that convert with other individuals requires that they be confirmed to an office called “member” and that they subscribe to the code of conduct of that body of believers. Confirmation can rightly require agreement to a code of conduct (including the paying of tithes to be considered a member in good standing), but baptism cannot specifically require anything other than the broad requirement of “repent of all your sins”, being those sins that you are aware of, and being that you forsake in your heart and confess the behavior as sinful, and not that you fully have modified your behavior yet (see our posts here and here).
Such modification comes after assistance from the Holy Ghost, or mind of God, as it is bestowed more fully upon the person who is baptized. Can’t you see how repentance only requires facing the right direction, and the heavy lifting comes from the Lord after one exercises their faith to be baptized? To expect a false interpretation of “forsaking sin” beyond merely a change of heart is to require the sinner to fully reform before having the grace of God to be able to do so. It is oppressive, and ungodly. To require a commitment to tithe before one is baptized (as opposed to requiring it before confirmation only) is to run close to priestcraft, and charging for ordinances. But, the LDS have merged baptism and confirmation as one ordinance, so hence the confusion (see our post here).
The novel (and more scripturally correct) idea is that you can be baptized first, and then confirmed much later if you are slow to reform your behavior after getting the mind of God. Confirmation needs a godly walk and conversation after baptism. The church articles are clear:
The duty of the members after they are received by baptism—The elders or priests are to have a sufficient time to expound all things concerning the church of Christ to their understanding, previous to their partaking of the sacrament and being confirmed by the laying on of the hands of the elders, so that all things may be done in order. And the members shall manifest before the church, and also before the elders, by a godly walk and conversation, that they are worthy of it, that there may be works and faith agreeable to the holy scriptures—walking in holiness before the Lord. D&C 20:68-69.
But, you can still be saved even if you are slow and don’t rise up to be a member yet. Therefore, get baptized and don’t fear! Let the increase of the baptism of fire and the Holy Ghost assist you in your quest to become more like God! Don’t worry about member status and obligations until you are ready. Consider also, that the Lord never intended the Word of Wisdom to be a requirement for membership, or temple attendance.