Python 3, 119 byte

def f(s,m,p): m,p=m.replace('-','').split(),p.replace('+','').split() for n,o in zip(m,p):s=s.replace(n,o);return s 

Input is a list with strings, replacement strings are space separated.

Example input: ['mississippi','-is -i','+iz +p']

Python 3, 93 byte

def f(s): s,m,p=s for n,o in zip(m.split(),p.split()):s=s.replace(n[1:],o[1:])  return s 

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Input is a list with strings, replacement strings are space separated.

Example input: ['mississippi','-is -i','+iz +p']