Does Israel's rejection of the Holy Spirit in Acts 7 apply to today's believers?
No. Acts 7 records God's dealing with national Israel, not the Gentile age. Israel rejected the Father, the Son, and then the Holy Spirit by stoning Stephen. That rejection has nothing to do with today's believers, who live in the Gentile age and are not under that specific dealing with Israel.
Les explains that Acts 7 continues Israel's pattern of rejection: they killed the prophets, rejected the Father, killed the Son, and now had the opportunity to listen to and come under the influence of the Holy Spirit, the third person of the Trinity. Instead, they stone Stephen, the Spirit-filled messenger. Les emphasizes that this was God's dealing with Israel and has nothing to do with us in the Gentile age. Verse 52 calls them betrayers and murderers; verse 54 shows they were cut to the heart and gnashed on him with their teeth. Stephen, full of the Holy Ghost, saw the glory of God and Jesus standing at His right hand. This passage concerns Israel's national rejection, not a pattern for today's believers.