Question

Many unicode characters modify the appearance of the previous character. is there one that
modifies the following character?

Answer 1

No, unicode only supports modifiers after the main character. From definition D52 in Section 3.6, Combination of the 6.0.0 specification:

• The graphic positioning of a combining character depends on the
  last preceding base character, unless
  they are separated by a character that
  is neither a combining character nor
  either zero width joiner or zero width
  nonjoiner. The combining character is
  said to apply to that base character.
• There may be no such base character, such as when a combining
  character is at the start of text or
  follows a control or format
  character—for example, a carriage
  return, tab, or right-left mark. In
  such cases, the combining characters
  are called isolated combining
  characters.