warning the DSMODT will replace the ingame file permanently, but you can restore your dark souls dvdbnd file again.
apperently an error could occur that some particles (including fog gate and enmy particles) on certain area will not appear in game or even have sound. 
the known place where this error occurs are: Undead asylum(also with stray demons fire), Valley of Drakes(no lightning on Drakes), New londo, Dukes Archive(also with the Channeler Soul Spear with no Sound), Crytal Cave(this is where it hurts. the prism stone will not appear, and so you cannot see the invisible bridge), Kiln of the First flame(this one is good for framerate whilst gwyn doesnt have fire sword. also including the brilliant light before soul vessel)
the good thing is you can look badass and cosplay the nameless king even though in pvp the other person will only see you using halberd
How to Install
-first, you need to have a DSModt v0.4 or newer by Nyxojaele and run it, then wait till its workspace generated
-at the DSMODT you will find a list containing map change the selection to Weapons
-Pick the weapon you need to replace with. i find the Halberd is best suited with move set and hitbox, even though its very light (if you wanted the icon i have only edited the halberd icon , so unless you want to replace another weapon and still have the icon, just edit the image named 60a2c243.png)
-after clicking at the picked weapon, click on the pencil icon at the top and name the new data anything
-the new data will be moved to user weapon. then on this new data drag and drop the DragonslayerSwordSpear.dae to the viewport
-after imported choose the material to m7_metal(dsb) as it works the best.
-after selecting the type of material there will be three boxes which is main, bump, and Specular. Drag and drop DS_D.png to the Main, DS_N to bump, and DS_S to specular.
-after everything looked ok click the button on top left and click on 'save to dark souls'
-if you want to replace the icon copy 60a2c243.png to dsfix tex_override folder. (its only on the halberd).
How to Uninstall
-Click on 'Restore Dark Souls' in DSMODT 
-or copy the backup of dvdbnd file if you have any
any known bugs
-Buff is placed at the bottom of your feet, probably because i havent put a bone but i cant fix it until i know the buff attachment name
-The running attack Hitbox is weird (probably because i use a halberd)

Credits:
RavagerChris37 for example with the bass cannon
Nyxojaele for DSMODT
Durante
Aatvark binder tool
Fromsoftware for dark souls and assets