Yea, the words are somewhat different, but that is of little consequence. The four gospel writers seldom record events or statements made by Christ in precisely the same way. In fact, some of them differ significantly. Certainly, none of them record the great commission in quite the same way. John's account of the great commission is the briefest of all. This does not mean that John's account was somehow tampered with or that part of it was deliberately removed. Nor does the fact that Mark's account mean that words were added at some later date because it differs from that of Matthew. There is absolutely zero MSS evidence to support such a claim. Consider how the other gospel testimonies support everything recorded in verses 9-20. For the sake of brevity, I shall keep my support texts to only one in each example.
1. Verse 9 says, "Now after He had risen early on the first day of the week, He first appeared to Mary Magdalene, from whom He had cast out seven demons.." John 20:1-13 confirms that Mary Magdalene was the first person Jesus appeared to after his resurrection.
2. Verse 10 says, "She went and reported to those who had been with Him, while they were mourning and weeping." John 20:18 says, "Mary Magdalene came, announcing to the disciples, 'I have seen the Lord,' and that He had said these things to her."
3. Verse 11says, "When they heard that He was alive and had been seen by her, they refused to believe it." Luke 24:11 says, "But these words appeared to them as nonsense, and they would not believe them."
4. Verse 12 says "After that, He appeared in a different form to two of them while they were walking along on their way to the country." Luke 24:13-15 records that while two of the disciples were walking Jesus suddenly appeared to them.
5. Verse 13 says, “They went away and reported it to the others, but they did not believe them either.” Luke 24:35-38 agrees with Mark that they did not believe. “While they still could not believe it because of their joy and amazement, He said to them, “Have you anything here to eat?”
6. Verse 14 says “Afterward He appeared to the eleven themselves as they were reclining at the table; and He reproached them for their unbelief and hardness of heart, because they had not believed those who had seen Him after He had risen.” Luke 24:35-41 also says that He appeared to the eleven and reproached them for their unbelief.
7. Verse 15 says, “Go into all the world and preach the gospel to all creation..” This is also recorded in Matthew 18:19, "Go therefore and make disciples of all the nations."
8. Verse 16 says, “He who has believed and has been baptized shall be saved; but he who has disbelieved shall be condemned.” John 3:18 says “He who believes in Him is not judged; he who does not believe has been judged already, because he has not believed in the name of the only begotten Son of God.” Acts 2:38 says, ““Repent, and each of you be baptized in the name of Jesus Christ for the forgiveness of your sins;”
9. Verse 17 says, “These signs will accompany those who have believed: in My name they will cast out demons, they will speak with new tongues.” In Acts 16:18, we see Paul casting out demons from a young woman. “This went on day after day until Paul got so exasperated that he turned and said to the demon within her, ‘I command you in the name of Jesus Christ to come out of her.’ And instantly it left her.” We also k now from 1 Cor 12, 13, and 14 that tongues as well as the other gifts were prevalent in the first century Church.
10. Verse 18 says, “They will pick up serpents, and if they drink any deadly poison, it will not hurt them; they will lay hands on the sick, and they will recover.” Paul being bitten by a “deadly serpent” in Acts 28:3-6 and experienced no harm. The healing of the sick through the laying on of hands is recorded in Acts 28:8, “And it happened that the father of Publius was lying in bed afflicted with recurrent fever and dysentery; and Paul went in to see him and after he had prayed, he laid his hands on him and healed him.”
11. Verse 19 says, “So then, when the Lord Jesus had spoken to them, He was received up into heaven and sat down at the right hand of God.” This is also recorded in Luke 24:51 and Acts 1:9. “And after He had said these things, He was lifted up while they were looking on, and a cloud received Him out of their sight.” Also, in Hebrews 1:3, “… He sat down at the right hand of the Majesty on high.”
20. Verse 20 says, “And they went out and preached everywhere, while the Lord worked with them, and confirmed the word by the signs that followed.” Hebrews 2:4 tells us “God also testifying with them, both by signs and wonders and by various miracles and by gifts of the Holy Spirit according to His own will.”
So, as you can see, verses 9-20 are well supported either in the other gospel accounts or in the epistles. The only thing that there is not a corresponding example for is in verse 18 which says “if they drink any deadly poison, it will not hurt them.” This does not however offer evidence of any addition or manipulation of the text. There is no justification for crying foul concerning anything that is said in these verses.