In[1]:= MAX = .5;
m = RandomReal[{0, 1}, {3, 3}]
Out[2]= {
{0.7511, 0.0403175, 0.356029},
{0.0846003, 0.417139, 0.894121},
{0.670992, 0.181403, 0.755288}}
In[3]:= n = m /. v_?NumericQ -> If[v < MAX, v, MAX]
Out[3]= {
{0.5, 0.0403175, 0.356029},
{0.0846003, 0.417139, 0.5},
{0.5, 0.181403, 0.5}}
In[4]:= f[v_] := If[v < MAX, v, MAX];
n = Map[f, m, {-1}]
Out[5]= {
{0.5, 0.0403175, 0.356029},
{0.0846003, 0.417139, 0.5},
{0.5, 0.181403, 0.5}}
