I just got a plastic iwb holster. I intend on using it for concealed carry of my Ruger lcp. The holster i got has a high side that goes against my skin and It comes up to somewhat of a point and poking my side.
How can ii or should i cut that side down and make it more comfortable? this was a used  and i paid $15 shipped  from ebay, they probably didnt like that high side either.

I have a blue lcp. I was thinking about adding some stainless steel pins  in place of the blue ones and maybe a heaver wolf recoil spring.

Could either of these modifications  cause a legal issue if i should have to use my pistol?

I have very few holsters that I haven't modified to work better for me.  As long as you aren't removing so much material that the trigger becomes exposed risking an ND from a foreign object,   you should be fine.    Early on I did my mods with a hacksaw and sandpaper before I owned a dremel, and they turned out fine.

Gun mods?  I vote no.   No to you facing legal problems because of mods in an otherwise good shoot.

I have modified just about every single one of my kydex holsters in some way, shape, or form.  Here is what I think you should know before changing.... Where eye protection when cutting the plastic and avoid breathing in the plastic dust.
Mock up with a pencil or some visibly removeable means to plot at what you want to remove or change.  
You can always remove more material but it is much more difficult to go back to previous state.
For rounding edges you can use a common file and just rough in the shape you want.  You will have some less than clean result so come back with sandpaper to get the excess roughness gone.  Once you have it to the shape you want and cleaned up of any roughage finish it off with a high grit sandpaper to polish it nice.
For removing larger portions I have used Dremel cutting wheel to rough in shapes but just be aware you can end up with hard angles you want to clean these up with rounded junctions of edges as this can be points where the holster can crack easier.  If you do not have a rotary tool with cutting wheel you can also use a hacksaw but like the cutting wheel cuts can leave those angle cuts and it is really hard to do clean rounded cuts so do the work to clean up when done.
Sometimes separating the holster is possible where you can take the front away from the back this makes moding easier but not all holster have this ability as they are riveted together.

Adding SS pins is up to you it should not be an issue.  Now increasing the recoil spring weight could induce malfunctions or make the pistol more ammo picky you would have to test to be honest as with any modification you can induce a problem or see no change/effect.  The real questions are...  What do you seek to get from the modification and after the modification are you going to increase the likelihood of malfunction or increase reliability?  Will the change have any effect that adds value (not monetary) for example will it help you shoot faster, better follow up shots, faster split times, or _____?