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We investigate the nonequilibrium electronic and lattice dynamics of the charge-density-wave (CDW) compound 1T-TiSe₂ using ultrafast optical spectroscopy over a wide range of temperatures and pump fluences. We reveal a close relationship between the observed ultrafast dynamical processes and two characteristic temperatures: T_CDW (∼202 K) and T* (∼165 K). Two coherent phonon modes are identified: a high-frequency A_1g mode (ω₁) and a lower-frequency A_1g-CDW amplitude mode (ω₂). While both modes soften with increasing temperature, in contrast to thermal behavior we observe a pronounced fluence-induced hardening of the CDW amplitude mode on sub-picosecond timescales. This anomalous frequency upshift provides direct evidence for a nonthermal reconstruction of the lattice potential, driven by transient screening of electron-phonon renormalization by the photoexcited carrier plasma. Concomitantly, the excited-state buildup time exhibits an abrupt increase above a well-defined critical fluence below the CDW transition temperature, signaling a qualitative change in carrier relaxation dynamics. The coincidence between phonon hardening and the fluence threshold indicates that ultrafast electronic screening reshapes the effective lattice potential underlying the CDW order, promoting a nonequilibrium metallic-like response without thermal melting. Our results establish ultrafast phonon hardening as a sensitive probe of lattice potential reconstruction and highlight the fragile balance between excitonic correlations and lattice dynamics in photoexcited 1T-TiSe₂.