There are several possible interpretations of Heb 6:
1- The warning is to Jewish people who had stopped short of trusting in Jesus for salvation after they had professed to believe in Him;
2- The admontion is hypothetical, that if it were possible to fall away after receiving all these things then to renew to salvation would require crucifying Jesus again;
3- The admontion is directed toward believers who have fallen so deeply into sin that they have crucified Jesus afresh and in danger of losing their rewards, not their salvation;
4- The admonition is to those so deeply into sin that they are in danger of losing their salvation
Since scripture repeatedly affirms the security of the believer, you can find direction as to which of the above four possibilities you favor. [Based on the following scripture teachings, one ought not interpret the admonition to read a saved person could lose their salvation ... 'made partakers of the Holy Spirit might be better rendered 'and were willingly being led by the Holy Spirit': John 3:15-16; John 10:27-30; Romans 8:35 & 8:37-39; Ephesians 1:12-14; Philippians 1:6; Hebrews 10:12-14; 1 Peter 1:3-5]
Reading especially Heb 10:14, we may know the salvation of the faither is secure when the Holy Spirit comes into the human spirit, not merely leads the seeker through the behavior mechanism but is on the Mercy Seat and dwelling in the human spirit, thus the faither is sanctified, as the Temple was sanctified when God was seated in the Holy of Holies.
One more paragraph of yours and then I leave you to try more of your doubt sowing without me playing ping pong over your offerings:
"Any person, at any time, has the ability to turn their back on God and conduct themselves in such a way as to exclude themselves from entry to heaven." Those not born again as Jesus taught to Nicodemus can reject salvation and remain unregenerate. But once you are born again, you are in God's family and His seed remains within you unto the end and the gates of Hell cannot prevail against that Seed, that 'earnest of your inheritance', such is the mystery of the magnificence of His Grace toward us!
<font color=black> "Every person should have the humility to recognize the weakness in them and strive to resist temptation lest they wind up going to hell, when people sin they force away the Spirit of God from them and all people need to repent when they sin to get that Holy Spirit back." Do you not realize that you have just affirmed Pauls teachng (#2 above) that it is impossible to re-crucify Jesus? If you could force the Holy Spirit 'seed' out of your human spirit, how many do you think are so skillful that they could of their own intellect defeat Satan and obtain salvation? Answer=zero, zip, nada, bupkiss ... that is why His Grace is so astonishing to behold, because while we were yet sinner Christ died for us, and should you be able to fail in carrying the Grace basket is not an option God offers because even sinless Adam could not resist the wiles of Satan, so I know self-righteous Mormons cannot. And for those, if they could fail to carry the Grace basket, Paul teaches clearly you cannot crucify afresh the Son of God for your readmission into His family. Your salvation is secure because it doesn't depend upon 'all you can do', it is God's work in you by the presence of His Holy Spirit!
<font color=black> "If you truly do have the Spirit of God with you and then sin, it’s absence will be noticeable to you." A quick study of the arrangement of the Tent Tabernacle might help you to realize why this sentence is in error. Even a gentile could come into the outer court and the temple not be defiled, and even if someone not a Jew came into the Holy Place, the Holy Place could be rededicated and cleansed, but if a Gentile defiled the Holy of Holies, it was the end of the life of the one entering in thusly, for God will not be approached by sinful flesh. The Holy Spirit indwells the spirit of the faither, Holy of Holies of the faither, and from thence administers change to the soul (behavior mechanism or Holy Place) and the body (the outer court of the Temple of the Living God ... for you are now in Christ Jesus the Temple of the Living God.<font color=black>
Have a pleasant evening, Grig. May God's spirit lead you until you receive the earnest of an inheritance in Christ and the Holy Spirit comes into your human spirit for ever and ever. Faithe in Christ and His Righteousness will be counted unto you. Faithe in 'all that you can do' and you will be lost. BTW, you are not the decider of your future exaltation of lack thereof, God is the author and finisher, Grig.