Formula To Substitute Given Symbols

I've got a workbook with multiple formulas e.g.:

t=S/D

TCh=Ch*(S^2/2D)*(D/Q)

TC=Co*(D/Q)+Ch*((i-D)/2i)*Q

which are built by implementing the symbols:

t, S, D, TCh, Ch, Q, TC, Co, i

I'd like to substitute the symbols in following sequence:

t = a
S = b
D = c
TCh = d
Ch = e
Q = f
TC = g
Co = h
i = x

Questions:

1) Which formula could substitute the symbols automaticly?

2) If there are up to 100 formulas in the workbook in the range of A1:E100,-

would it be possible to to set the substitution for the mentioned range?

See the attachment.