How to replace matrix NaN with string from cell array

I have a cell array of strings which includes some unmarked numbers and some marked with '#':

cell = {
    '# 2.537'    '1.219'      '0.457'    '0.214'    '# 0.120'    '0.245'
    '3.244'      '# 1.400'    '0.649'    '0.515'    '0.207'      '0.075'}

I want to convert the cell to a data matrix and do some calculations for instance multiply with 2:

data=str2double(cell)*2

This will leave the numbers marked by '#' with the 'NaN'. Finally, I want two things where I need some help: 1) replace the 'NaN' with the original numbers marked with '#', for instance '# 2.537' into data(1,1), and 2) convert the data matrix into a cell array of strings. The order of step 1 and 2 is not important.

the output should be:

output = {
    '# 2.537'    '2.438'      '0.914'    '0.428'    '# 0.120'    '0.490'
    '6.488'      '# 1.400'    '1.298'    '1.030'    '0.414'      '0.150'}

Thanks in advance