Let me clear something up first. The first expert advised
"If you feel inclined to file a tax return, the IRS is not going to refuse to process it. They will definitely take your check." You have received 2 responses from 2 different experts.
Your concerns are much more clear now with your inclusion of the following:
"But its not that easy because the 1040 might show that I do not owe any taxes but because of the EIC, the Child Tax Credit and the Additional Child Tax Credit the IRS might be the one sending a check!"
The IRS will process and correct a return you send. Generally, if you are a bona fide resident of a U.S. possession, you cannot claim the EIC on your U.S. tax return. However, certain U.S. possessions may allow bona fide residents to claim the EIC on their possession tax return.To claim the EIC on your U.S. tax return, your home (and your spouse's if filing a joint return) must have been in the United States for more than half the year. If you have a child, the child must have lived with you in the United States for more than half the year. For this purpose, the United States includes only the 50 states and the District of Columbia. Special rules apply to military personnel stationed outside the United States. For more information on this credit, see Publication 596, Earned Income Credit.
Child Tax credit is determined on your Modified Adjusted Gross Income. For purposes of the child tax credit, your modified AGI is your AGI plus the following amounts that may apply to you.
Any amount excluded from income because of the exclusion of income from Puerto Rico. On the dotted line next to Form 1040, line 38, enter the amount excluded and identify it as "EPRI." Also attach a copy of any Form(s) 499R-2/W-2PR to your return.
Any amount on line 45 or line 50 of Form 2555, Foreign Earned Income.
Any amount on line 18 of Form 2555-EZ, Foreign Earned Income Exclusion.
Any amount on line 15 of Form 4563, Exclusion of Income for Bona Fide Residents of American Samoa.
If you do not have any of the above, your modified AGI is the same as your AGI.
So in short, if you are resident of PR you are not allowed to claim EIC on your US tax return and the Child Tax Credit is handled differently too. The IRS will not refuse to process but they will refuse a credit that someone is not entitled to under US tax law.
The first quote I know to be correct (except the part within parenthesis that is THE issue.
The return can be filed and the IRS will process but they will correct if necessary.