Another Variant?

Answer, YES it is also designated as VFA-98, the final and ultimate one man army VF series of aircraft. It used the VF-39 as a airframe and modified in various ways. The twin tails fold slightly outwards at high speeds and ventral fins will move and are slightly bigger. Aircraft performance will be slightly decreased for the addition to TVC for PSM capabilities to surprise those who dare challenge you.

Story+ Encounter

First encounters of this aircraft was after around the time of Vipers disappearance after the engagements of a Intruder ace. He was brought our of the war briefly for testing of a new aircraft that his new 'furry' body has taken. only one account of many sightings of Viper after his missing.
Retrieving data from incident with a terrorist squadron
Merc One: <<Ah hell, one enemy aircraft. looks like Veredalian IFF>>

Merc Two: <<Don't tell me its that famed Wild Hellhound..>>

The two ship of Merc aircraft merge with the fighter and the VFA did a 180 on the spot and engaged.

Merc Two: <<Dammit it is him, it's Viper!>> Attempts to keep his nose on Viper's aircraft

Viper: <<You dare have the nerve to fight in this state you two>> Pulling high AoA on Merc Two, Both circling each other like dancers in the sky

Merc One: <<Screw this I'm out, good luck on you Merc Tw- static>>

Viper: <<Merc One Down, Merc Two... Leave the AO>>

Merc Two: <<...Yes sir>> After a few minutes, Merc Two left AO and the incident ended

Weaponry list for aircraft

Multipurpose Directional Micro Missile [MDMM]
dangerous missiles that fire in bursts at targets, lack of speed makes up for insane tracking
XEML 'Excalibur'
Large railgun that can use standard or explosive RD121 rounds, can take out the strongest of flying fortresses
Advanced Standard Missile [ADSDTM]
Can replace your standard missile with improved one with increased power, homing, speed and lock on range.
Thermobaric Bomb [FAEB]
Powerful dumb weapon that uses oxygen as a combustible source and large blast radius [can be used to kill flying airships with enough skill]
Hyper Fire Cannon [HFC]
New cannons that fires super fast with high damage with every hit. Addition with a new targeting computer for aiming the guns in dogfights.