Easy yes!, just delete the autocannon weapon out of the ships entity file & paste in 1 copied from a laser weapon.

So in the ships entity file delete;

Weapon
    WeaponType "Projectile"
    damageEnums
        AttackType "CAPITALSHIP"
        DamageAffectType "AFFECTS_SHIELDS_AND_HULL"
        DamageApplyType "BACKLOADED"
        DamageType "PHYSICAL"
        WeaponClassType "AUTOCANNON"
    DamagePerBank:FRONT 27.000000
    DamagePerBank:BACK 49.500000
    DamagePerBank:LEFT 49.500000
    DamagePerBank:RIGHT 27.000000
    Range 5000.000000
    PreBuffCooldownTime 4.500000
    CanFireAtFighter FALSE
    SynchronizedTargeting FALSE
    PointStaggerDelay 1.000000
    TravelSpeed 4000.000000
    Duration 0.000000
    fireConstraintType "CanAlwaysFire"
    WeaponEffects
        weaponType "Projectile"
        burstCount 15
        burstDelay 0.060000
        muzzleEffectName "Weapon_TechCapitalAutoCannonHeavy_Muzzle"
        muzzleSoundMinRespawnTime 0.770000
        muzzleSounds
            soundCount 3
            sound "WEAPON_TECHCAPITALAUTOCANNONHEAVY_MUZZLE"
            sound "WEAPON_TECHCAPITALAUTOCANNONHEAVY_MUZZLE_ALT1"
            sound "WEAPON_TECHCAPITALAUTOCANNONHEAVY_MUZZLE_ALT2"
        hitEffectName "Weapon_TechCapitalAutoCannonHeavy_Hit"
        hitHullEffectSounds
            soundCount 1
            sound "WEAPONIMPACT_PHYSICALHEAVY_HITHULL"
        hitShieldsEffectSounds
            soundCount 1
            sound "WEAPONIMPACT_GENERICHEAVY_HITSHIELDS"
        projectileTravelEffectName "Weapon_TechCapitalAutoCannonHeavy_Travel"

Then in its place paste in;

Weapon
    WeaponType "Projectile"
    damageEnums
        AttackType "CAPITALSHIP"
        DamageAffectType "AFFECTS_SHIELDS_AND_HULL"
        DamageApplyType "BACKLOADED"
        DamageType "ENERGY"
        WeaponClassType "LASERTECH"
    DamagePerBank:FRONT 45.375000
    DamagePerBank:BACK 0.000000
    DamagePerBank:LEFT 0.000000
    DamagePerBank:RIGHT 0.000000
    Range 5000.000000
    PreBuffCooldownTime 5.500000
    CanFireAtFighter FALSE
    SynchronizedTargeting TRUE
    PointStaggerDelay 0.900000
    TravelSpeed 2000.000000
    Duration 0.000000
    fireConstraintType "CanAlwaysFire"
    WeaponEffects
        weaponType "Projectile"
        burstCount 1
        burstDelay 0.000000
        muzzleEffectName "Weapon_TechCapitalLaserHeavy_Muzzle"
        muzzleSoundMinRespawnTime 0.100000
        muzzleSounds
            soundCount 2
            sound "WEAPON_TECHCAPITALFIREBALLHEAVY_MUZZLE"
            sound "WEAPON_TECHCAPITALFIREBALLHEAVY_MUZZLE_ALT1"
        hitEffectName "Weapon_TechCapitalLaserHeavy_Hit"
        hitHullEffectSounds
            soundCount 1
            sound "WEAPONIMPACT_PHYSICALHEAVY_HITHULL"
        hitShieldsEffectSounds
            soundCount 1
            sound "WEAPONIMPACT_GENERICHEAVY_HITSHIELDS"
        projectileTravelEffectName

You can put weapons in from other race's too if you like.

NOTE; when you do this make sure you change the DamagePerBank:FRONT, BACK, LEFT, RIGHT to corespond with that of the weapon that was originally there. For instance, you will notice that the laser weapon above only has a value for DamagePerBank: FRONT. If you want all the weapons that Autocannon weapon used you will need to add values to the BACK, LEFT & RIGHT to the laser weapon you have put in its place, as it is in the AutoCannon's.

It wont effect the balance much at all if you have those DamagePerBank values similar to the AutoCannon's.

Actually, those modifiers are based on whaich ship types are being hit with what.  (LRF Kills LF and so on)  The weapon types are cosmetic.

-Twilight Storm

@ CursedSpirit,    I would not recomend doing it that way. What about the travelSpeed and duration. If you put a beam weapon effects onto an auto cannons, it will have a travelSpeed of 4000 when it should be 0. The duration will be 0 when it should be 4. So effect wise your beam will last for 0 seconds. You may get away with swapping an autocannon with a laser because they are both projectile type, but even then the DamageType is different.

The string file is in text format, its just a re-named .txt file.

I figured out how to open the string file even though it is a .str file.

Super Zero the super mod hero has answered all my questions via PM.