Capulet does change his mind about Juliet's marriage to Paris after Tybalt's death. From the start, Capulet was not in favor of the marriage due to Juliet's age, although he did approve of Paris as a suitor. He states in Act 1 Scene 2, "My child is yet a stranger in the world, she hath not seen the change of fourteen years.” However, even though he objects to the marriage due to Juliet’s age, he does give Paris a chance by stating, "But woo her, gentle Paris, get her heart; My will to her consent is but a part. An she agree, within her scope of choice lies my consent and fair according voice (lines 16-19). Here Capulet is stating that Paris should try to win her affection, and that he will give his approval to the one suitor she chooses.
However, after Tybalt’s death there is much mourning in the Capulet household. Paris comes once again to speak of marriage. During his visit, Capulet decides that the best thing for Juliet during that sad time is to bring her joy through arranging her marriage to Paris. Juliet's mother confirms this when she excitedly tells Juliet, “Well, well, thou hast a careful father, child; one who, to put thee from thy heaviness, hath sorted out a sudden day of joy that thou expects not nor I looked not for” (Act 3, Scene 5 lines 120-125). Of course, Juliet is already married to Romeo (although her parents do not know this) and she refuses to marry, thus enraging her father due to her disobedience.
Capulet never changed his mind about the marriage. From the start, he was approving of the match and encouraging of Juliet's suitor. In Act 1.2.16-22, Capulet says:
But woo her, gentle Paris, get her heart,
My will to her consent is but a part,
And she agreed, within her scope of hoice
Lies my consent and fair according voice.
This night I hold an old accustomed fast
Whereto I have invited many a guest
Such as I love, and you among the store.
When Tybalt is slain by Romeo, Lord Capulet erroneously believes that a hastened marriage to Paris will cure his melancholy daughter. In Act 3.4.13-16, Capulet pleads:
Sir Paris, I will make a desperate tender
Of my child's love. I think she will be ruled
In all respects by me; nay, I doubt it not.
Lord Capulet, blind as ever, believes until the bitter end that his daughter will ultimately follow his "will."
He wasn't planning on marrying Juliet with Paris. Lord Capulet thought that by Juliet marrying Paris would cheer her up and stop crying all the time but she's really crying beacuse Romeo was banished out of Verona.